I'm very impressed with ubuntu lately. Despite all the drama in the blog space about their technical decisions, from a user's perspective it's a very stable and mature OS. Every upgrade fixes a few little things, makes things a little bit better, and most importantly doesn't break anything. There's very little to get excited about and very little to get annoyed about. It really does just work. On windows or even mac I would wait until a day when I don't have a lot of work that needs to get done to install a new version of the OS, on ubuntu i feel confident clicking okay on the upgrade notification, even if i'm in the middle of something important.