I’ve put my hand on Windows 7, and I was fortunate to be able to install the 32-bit version in my old desktop machine, purchased last 2003. Then, with my newer (1 1/2 yr or so) laptop, I was able to test the 64-bit version. These are both Windows 7 Ultimate OSes.
So with those 2 versions come problems that are uniquely their own, specific to the 64-bit OS: though basically breaking the 3GB RAM barrier, I immediately faced the problem of Zonealarm firewall not being able to install, so I searched, and sure enough, we have PC Tools Firewall Plus free edition to take its place. AVG 9 has a free version for Win 7.
The rest, they work. The main precaution when thinking of installing 64b Win7 is antivirus and firewall softwares. The rest of the softwares, they usually work – I was able to install back my old softwares (Harmony Assistant, Noteworthy Composer, CCleaner, Defraggler, etc) without a single issue being encountered.
So I’m now on Windows 7.