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Running Fusion is, for now, a mix. On the user feature count, I'd have to say that Parallels is still out in front. Aside from the things in Fusion that are still in the "Not yet implemented" state, Parallels is just better designed to fit in with your Mac OS X desktop.
The big reason here is Coherence. Being able to just click on a Windows application in the Mac OS X Dock, and have it come up is A Good Thing. However, Fusion wins for me in how it treats your OS X system. First, unlike Parallels, it doesn't install various kernel extensions in /System/Library/Extensions. So, if Fusion decides to fall down and go boom, it's harder for it to take your Mac OS X host operating system with it.
I know that on a "feel" basis, my Mac OS X host OS "feels" more responsive when I'm running Fusion than when I'm running Parallels. Parallels, at least on a first-generation MacBook Pro with 2GB of RAM, puts a whack on your system. Regular pauses where nothing's quite working, switching between Mac applications can take a long time, etc. In comparison, Fusion seems to abuse my Mac OS X host environment far less. Of course I don't get Coherence, and there's this odd bug wherein if you change primary IP addresses, the vmnet-bridge process starts complaining bitterly to system.log at a fast clip. That however, is to me, a beta bug, so I'm not to worried.
While I don't know for sure every aspect of who Fusion is targeted at, for now, it appears to be more of a product for those who only need to run a VM or multiple VMs occasionally, while Parallels seems to be more for those who need to have their primary VM running constantly. While I'm positive that Parallels doesn't abuse a Mac Pro nearly as much as my laptop, I'd hesitate, based on my experience, to run multiple VMs with a lot of Mac OS X applications running, especially Rosetta applications.
While it's not soup yet, the latest beta of Fusion is showing a lot of promise. It runs well, and doesn't abuse my system any more than it has to. That's always good.