Bob Cringley argues that the time factor in upgrading to Win7 is intentional:
have you actually done a Windows 7 upgrade? Mine took seven hours! It shouldn’t have to take that long unless part of the goal was simply to discourage upgrading.I had thought of just doing a clean install and starting from scratch, but I do have some files that I don't keep on my external drive, and some of my app settings take a few minutes to configure. Besides, I kind of wanted an excuse to use an awesome site called Ninite that has a lot of the apps I'd need to reinstall on one page.
My first impressions so far are good. My box wasn't exactly straining to run Vista (strong dual-core 64 bit CPU, decent video, and 8 GB of RAM), but now the boots and system processes are faster. The usability is good, but I haven't spent enough time to see the improvements I've heard others talk about.
Overall, I'm pretty impressed actually. Congrats, MS!