On my MacBook Pro Core2Duo 17" with 2 GB of RAM, I have used Parallels since it first came out and I am very satisfied with its performance, functionality and stability. Here is how my VM is configured. This VM was created using the initial version of Parallels and it is the same VM I am now using with Parallels 3.0. 512 MB of memory 20 GB (partitioned as two drives inside Windows XP) Sound is on CD set to not auto connect USB set to not auto connect Coherence mode is turned on Here is what I run inside my VM. My usage philosophy is to use the VM only for apps that I don't have equivalents for in OS X. Windows XP Professional with all updates installed ESET NOD32 Antivirus Cisco VPN Client 4.8 Microsoft Money 2006 Deluxe using data from share Mac home directory Microsoft OneNote 2007 Paint Shop Pro Remote Desktop Connection client Microsoft VisualStudio 2005 Professional Windows Media Player to play DRM protected videos My Parallels VM runs all the time. I don't suspend it and the only time I reboot it is to install Windows updates or to back up my MacBook Pro to my external hard drive. It is also very rare for me to reboot my MacBook Pro. With Parallels and my VM running, I put my MacBook Pro to sleep by closing its lid when I am not using it. Not once have I experienced any performance degradation on my MacBook Pro while running Parallels. OS X appears to be just as snappy with my VM running as it is when my VM is not running. I have also experienced no issue with regards to putting my MacBook Pro to sleep with my VM running. It goes to sleep normally and wakes up without any issues. I don't run any games in my VM (I have an Xbox 360 for that) and I don't attempt to connect USB devices to it (all my devices are supported quite nicely under OS X). I did install the latest beta of VMWare Fusion to see how it compares to Parallels 3.0 and at this time, I see no reason to switch. Parallel's implementation of the Start menu in my OS X task bar is one of the clear advantages Parallel's currently enjoys. I will fully acknowledge that your mileage may vary. This is certainly dependent upon how you use your VM.