VMWare has specifically tweaked Fusion to work well with Lion. For example, when you're running Windows in Fusion's Unity mode (which makes Windows apps appear as individual programs, just like your Mac ones), each of your open Windows apps appear separately in Mission Control. You can also optionally add Windows programs to Launchpad. Thankfully, Fusion does so intelligently: It doesn't add every single Windows program to that app interface.
I had no trouble at all running a normal suite of Windows office applications (including Microsoft Office, Internet Explorer, and Acrobat). The applications loaded quickly; everything worked as I expected it to. I also tested a number of games, and there the results were decent. Most older games ran just fine, and more recent games ran reasonably well, but graphically-intensive new games ran either very poorly or not at all. For example, the demo of Hard Reset ran at such slow frame-rates that gameplay was virtually impossible. That same game is playable in Parallels 7; I'd attribute the difference to Fusion's support for only 256MB of video RAM, versus 1GB in Parallels.
Hardware peripherals worked well: Fusion detected when I plugged them in, and offered me the choice of using them with either the virtual machine or the host Mac. The iSight camera worked in Windows, too.
Fusion includes a 12-month subscription to McAfee VirusScan Plus for virus protection; a full year of coverage is nice if you opt to go with a third-party solution. For this review, though, I opted to use Windows' own (optional but free) Security Essentials, which seems to be doing the job so far.
Generally, using Windows 7 in Fusion 4 was marked by an absolute lack of drama. Applications simply ran--and ran well. I had no crashes, and the occasional Windows update installed without trouble. I played some high definition video clips in Windows Media Player, and they played back with clear video and stutter-free audio. In short, Windows 7 and Fusion 4 work very well together.
Other operating systems
Windows isn't the only OS you can run under Fusion. New in this release of Fusion is the ability to install OS X Lion itself as a virtual machine. To do so, you simply point Fusion's new virtual machine assistant at the Install Mac OS X Lion.app file that you get when you purchase Lion from the App Store. (If you didn't keep a copy of this file, you can download it again.)