I just upgraded Parallels Desktop for Mac to v3.0, and I love it. I was impressed with Parallels 2.x, but this is quite an improvement.

• I can run OS X, XP and Vista all at once, very smoothly. Haven’t tried Ubuntu, yet, but it should work.
• Coherence (as in 2.x) hides the guest OS window, so every application appears as though it’s running under OS X.
• I have complete drag-and-drop and clipboard transparency across all operating systems.
• I can transparently open files in any environment from any other.
• I can run CPU-intensive and (some) hardware-dependent applications like SoundForge. [I get audio input from Firewire devices like MOTU interfaces, but I can send audio output from Windows through the OS X audio system.]
• Memory and CPU loads appear to be reduced from 2.x.
• The new snapshot feature (with versioning) is handy and fast.
• Installing/upgrading was straightforward.

Decades ago, I used to write system software similar to what the folks at Parallels have developed. We didn’t have help from things like Intel Virtualization Technology in those days, but this is still tricky stuff. I think I’m qualified to say that this is a very well-executed product. Kudos.

Update: I should add that I’m on a hefty box: Two dual-core CPUs, 4GB RAM, 1.25TB disk on three drives.