I'm a developer who bought a Mac a few weeks ago for the same reasons... and am happy I did so.. Its nice to have a "real" machine

that has unix underneath the user friendly hood.. Most places offer some sort of return policy so you could always return it (potentially minus a restocking fee if you aren't careful to check for that before you buy).
I figured that worst case Bootcamp was safe to bet on re: either that it would work now or soon and at least I could boot either one (or boot my old PC)... and Bootcamp worked fine for me with Vista.
Now with the newest parallels release I've got the ideal setup working..a windows task bar at the bottom of one of my monitors.. and the Mac's dock on another..
I admit to worrying a bit when I encountered glitches getting Parallels to work.. but I was pushing the envelope using Vista and with the version 3 release using Parallels with the Bootcamp installation..and it seems to work just fine for me now after the lastest release (posted in the forum but not on their main download link yet). The glitches I encountered were mostly getting it configured and tools installed so it would complete the boot.. but after that it works great so I suspect the core code is solid.
I think getting away from the level of bugs/annoyances running MS Windows on a PC made it worth some initial hassles getting things setup on the Mac. Now if some program misbehaves and screws up windows requiring a reboot.. (or hassle waiting for something chewing up all the CPU) I can be working on the Mac while it does so since it only hands the virtual machine 1 CPU to work with

I hadn't tried it.. but it could even speed up working with Vista by keeping another windows VM around so one is always functional while waiting for the other to reboot or get to where you can kill the misbehaving program thats hogging CPU..
Judging from the lack of glitches once its properly configured to run and boot (and using the versions that actually support Vista now

) I'm suspect the situation is that the company likely has a core group of good engineers getting the main virtualization core working well and seems safe to use once its booted.. However it appears is being let down by the rest of the team (eg, their highest support priority should be answering concerns on these msg forums since a posting here helps multiple people vs. a reply to a single email may only be helping more than one.. Both need to be done, but the point is if if you are too swamped to handle everything well then the public forum should take priority since it likely will cut down on the number of individual emails received... Additionally adding issues to a public FAQ file helps more people than the same reply in 1 individual email..)
. Likely perhaps the core team testing with their own internal configurations of virtual machine settings and perhaps letting some less skilled folks handle develoing some of the easier code re: eg the user interface to create the configuration, etc.. gui types.. and then poor QA folks not testing enough options and poor documentation and support staff.
eg, there is no documentation in the main docs on how to handle having multiple disks wth Bootcamp partitions (it doesn't know which one to use unless you edit the configuration file manually).. even though the information is findable from a search of the forums.
I suspect it partly depends what sort of tasks you are doing and what sofr of machine you are looking at buying. Ok, I'll admit I doubt I may not have done it for an 1 Gig iMac like you mentioned watching demo Parallels (though you didn't say that was the model mac you were looking at.. just that it ran a demo).. I was lucky enough to be in a position to upgrade to a decent machine and was lured in and by the call of an 8 core Mac Pro and adding 8 gig RAM.. (nice to have a machine use 10% CPU when doing things my old windows box might have been grabbing 100% for.. and its only a year old dual core) Also I'm doing platform independent code at the moment and have less need for ms-windows specific stuff at the moment and may be able to make use of the extra cores and ram.
I suspect its a small company overwhelmed by the demand to have the product quickly and a large customer base all at once before the company and software had time to shake out some of the bugs that often arise when you release even well tested software out to lots of folks whose software and hardware environments are going to vary more than you could test for in the lab... and btw I note that many of the comments in this forum overall were about beta software (or new features of released software still in beta).
eg, at least for me once I got parallels to work in windowed mode.. allowing me to resize the window, etc, it worked just fine in that mode.. but it wouldn't enter coherence mode.. At least in my case what was needed was an undocumented step (hadn't searched the forums to see if others ran into this) where I had to set a custom display mode for vista matching the resolution of the monitor it was running on. That isn't documented anywhere stilll, and there are still minor workarounds to get it initially functional. eg it inexplicably complained about not being able to allocate virtual memory and wouldn't start the guest OS (regardless of whether I checked the box to tell it to preallocate).. when I've got 9 gig of RAM in my mac and lots of disk space. I had to lower the video card memory from 64MB down to like 16MB... but then after it booted for the first time was able to switch it back up to 64MB and have it work fine from then on.. (though I also needed to lower the main memory allocated to the virtual OS from the high of 1500MB down to 1400MB (actually I think it can be a bit higher than that but hadn't played with it.. I think its likely they are making it a maximum of 1500MB total memory including video memory and a little extra.. but it doesn't document this anyplace and the interface shouldn't let you configure things that won't work);.
There was also a glitch before the most recent version at times getting it to initially read the Boot Camp drive I figured was a Vista thing... (though I discovered if it complains it can't read the drive and the VM stops.. I tell it one more time to start and this time it will.. .again a startup issue.. once it starts its great..).
I also panicked when I came to these forums and saw some of the msgs wondering if I'd been a bit tooo premature.. but now that its working I do have the impression its like most software which most people use just fine and yet a minority who do have problems will be vocal on forums posting about it... In many cases the posters are people who have tried to push the envelope doing things like running Vista, etc.
The one glitch left I can't get to work is something I can get along with out. I suspect I'll need to wait on a fixed update from Parallels.. is that coherence only works for me in single monitor mode still (for me thats fine since I don't need windows that much, it is a 20" monitor and I can always move it over to 24" one if I need more.. if I ever feel like I need all 3 monitors for Vista I'm likely focused enough on it that I can boot into Bootcamp instead for a bit..) I'm hoping they'll get this fixed soon though so I just put windows from whichever anyplace on any monitor. (it sounds like it works for people with only two screens.. with the third screen given their size the fake display it tells Vista about is apparently too big for it to handle (though I'm not sure why.. with 64MB of video memory configured.. but the combined width of all the monitors is 5200 pixels (by 1050 or 1200 high).