I too have a bunch of machines, but I did the update for most of them. I started way back when the RTM first came out though, so it was easy to do it and take some time. The key is to have multiple hard drives, so that you can switch them out and keep using the machine with the old system until the new one is ready.
Also... If you haven't ever used it before, Ninite is an absolute lifesaver:
http://ninite.com/Anyhow... Since I could only vote for one, I thought I'd list out all of my Windows machines as they currently stand:
Home Server/Man-Cave Box: Windows 7 64-bit
Home Office PC: Windows 7 64-bit
HTPC: Windows 7 64-bit
Laptop: Dual Boot OSX 10.5 (Leopard) and Windows 7 64-bit (Macbook Pro)
Netbook/Tremote: Windows XP
Work Office PC: Windows Vista 32-bit
Main Video Workstation: Dual Boot OSX 10.6 (Snow Leopard) and Windows 7 64-bit (Mac Pro)
Video Wall PCs (2 of them): Windows Vista 64-bit
Video Wall Server: Windows XP
Let me tell ya... Windows 7 absolutely SCREAMS on my 8-core (16 with Hyperthreading) Nehalem-based Mac Pro with 8GB of RAM. I don't have MC installed on it or else I'd run the JRMark benchmark on that sucker. Maybe later.
All in all, I really LOVE Windows 7. I was fairly lukewarm on Vista (not impressed at all when it first came out, though they fixed much of its problems with subsequent service packs). Windows 7 is a good advance, though. It really reminds me of the Windows 2000 vs Windows XP thing. Windows 2000 was great under the hood. They did a fantastic job re-writing the core of the OS for that release. However, it wasn't really ready for consumer use. I used Windows 2000 on one of my systems at home way back then, but I always had to dual boot it to Windows 98 because there were some programs that wouldn't run at all on it (and others would run noticeably worse). Windows XP fixed most of that and added the "chrome" that consumer desktop users needed.
Windows Vista vs 7 is much the same. It is essentially the same OS at its core, but they've tweaked just enough to make it WAY better.
And don't believe the haters. The new taskbar is fantastic. Of course, I'm an OSX user so...