Installed Parallels build 5160 today on a clean install of 10.5 Leopard. Issues so far: Hard drive containing Bootcamp partition disappears from finder when it is assigned as a second hard drive in Windows XP Guest OS and is unrecoverable until a reboot (of Mac OS). Random crashes, including several that needed a hard reset (shutting down using the power button). Drivers failing, file systems timing out. Windows XP will not shut down after use (Parallels needs to be killed via a force quit) None of the above happened in Tiger. Let me emphasize that this is a clean install of retail Leopard, on a factory standard 2.66 Quad Mac Pro, with nothing else installed at this point except iWork. If it was going to work, it would work on this machine. SWSoft need to start issuing some clearer guidance that the latest build is not even what I would consider beta ready. If you rely on Parallels, I would recommend sticking with Tiger until further improvements are made. Fortunately, the machine I tested on is just a spare.
those issues are pretty much the same on 10.4. you can try seeing if the build 5162. see... http://forum.parallels.com/showpost.php?p=86130&postcount=12 solves it. or if you can get your hands of build 4560, I hear reports on this forum that it is working good under leopard.
Those issues may also occur for some people on Tiger. The point I was making though is that these problems didn't occur on the same machine, with an identical setup running 10.4. The only difference in this case was Leopard. A previously very stabe install of Parallels was rendered almost unusable. I'll keep trying new builds on our Leopard test machine, but we're not planning to jump to 10.5 anytime before the end of the year anyway.