All of the upgrades and reinstallation are done, and I now have a zippy essentially-new machine running Windows 7.
The most obvious change in 7 is in the taskbar. It uses large icons instead of a small icon and window title, all open windows of the same type are always consolidated into a single entry on the taskbar (previously it would only consolidate them once it started running out of room), and you can pin a running program to the taskbar in order to launch it again later. It’s basically a lot more like OS X’s Dock now.
The Explorer has also changed a bit. There’s no more ‘Explore’ option off the computer icon’s context menu, which is kind of annoying. And they’ve removed the tree view from the Explorer windows (but you can reenable it in the folder options), instead using the sidebar to emphasize a bunch of standard locations like your home directory, your music directory, network servers, etc. Which is also a lot like how Finder works…
Otherwise, things have gone fairly smoothly, and I haven’t really had any problems that I can attribute directly to Windows 7 itself. I still have to poke around and explore what else might be new, though.