Well, I took the plunge last night. I meant to upgrade one of my least used blogs to Wordpress 2.1 as a test, and it was so quick and easy I ended up doing all four. Basic process was just backup the database, disable all plugins, copy the upgrade into the same directory as your main install, run the upgrade, restore the plugins. Quite painless.
I still think that Wordpress needs to built the upgrade functionality in, I should be just clicking to install it and run the above process. That is the sort of thing that takes away the admin side of Wordpress, and would draw more people into using it.
Overall, it seems a little faster, a little prettier, and nothing has broken. So, happy with it thus far.