The new Ubuntu 7.04 "Feisty Fawn" beta CD image won't boot at all in Parallels. It freezes on a black screen after I hit enter at the boot prompt. It boots OK and installs successfully in VMWare Fusion, however. I've always noticed a difference in the way Linux boots in Parallels vs. VMWare. Under Parallels I get the text mode boot screen. In VMWare, as it does on a real machine, it boots with the usplash graphic image and progress bar. Part of the Linux project I'm working on involves customizing the boot splash image, so I can't test it at all in Parallels.
I also found this issue shortly after Feisty beta came out. It is an issue with a CD virtualization change made by Parallels that the current infestation of the linux kernel in Ubuntu does not handle properly. The issue actually appeared in Feisty Herd 5 with the newer kernel versions. Additionally, the issue happens with the latest kernels in the Fedora 7 test releases. If you want to help get this fixed, check out my bug report here: https://launchpad.net/bugs/95830