Virtualization solution from Parallels (called Parallels Desktop 3.0 for Mac) allows nice integration between Windows and your Mac.
Parallels call this feature ?Coherence? for its ability to hide the Windows desktop and make it appear as if your Windows applications are running directly on your Mac. VMware Fusion also has the same feature called ?Unity?. It also works very well, although not with Windows Vista, yet.
Coherence completely blew the broad between Windows and Mac and allows users to get the best of both worlds at the same time. It works really very nice! With this feature Parallels Desktop now goes even further to deepen OS integration and create a seamless user environment.
Parallels Desktop is better integrated into the Mac OS desktop by means of registering file types with the Parallels guest applications, MS Office applications could be opened by simple clicking on them. You can also get Windows notifications on the Mac desktop - that is very cool.
Parallels set up shared folders between OS X and Windows quite nicely. Fusion asks you to do this manually.
Fusion lets you access Windows programs from its Applications menu. Parallels let you run programs from its Applications menu or the dock icon.
You can open Mac files with Windows apps and Windows files with Mac apps (which means you have the ability to choose).
For some time working with Parallels you can almost forget that you're running two OSes!
Parallels have Snapshot Manager feature which lets you save a copy of your virtual machine at a point in time. You can create a snapshot for a stopped or running virtual machine. When I created a snapshot of my Windows XP, it took about 23MB. Parallels also have a nice UI for managing the snapshots. You may have any number of snapshots and they can all be managed nicely. VMware also has snapshots, but they seem less robust.
The capability of Parallels is more likely, you just don't notice that you are working with virtual machine, it seems to be just a real machine with real applications. Parallels Desktop has nice usability.
I pretty satisfied with Parallels, especially since they have a fairly active support team with forums, knowledgebase and all the other necessary stuff. I stand with Parallels!