If you have Vista, uninstall 5 before you install 6. Especially if you have a lot of skins. Otherwise, this will happen:
Yesterday I booted in to Vista only to discover that almost every program that ran on startup crashed, followed by "Network Command Shell has stopped working".
At first I thought this had knocked out my networking because my Internet wasn't working.
I was looking all through my network settings and router settings trying to see if anything was wrong but it was all working kosher.
After a lot of debugging I noticed 64 bit applications could access the Internet. IE7 x64 was successfully surfing. So I did a search for x64 related Internet issues.
Turns out it's all NOD32's fault. Uninstalling NOD32 and rebooting fixed it. Fuckin' thing. Now I'm Anti-Virus free and I'm Lovin' It.
Looks like it's only an x64 issue. Unfortunate, after using Vista x64 for a couple of months now there doesn't really appear to be many reasons to keep it over the 32bit alternative