It's alright, but it's still got a long ways to go; the goal of Ubuntu and GNOME/KDE was to make more inexperienced users be able to use Linux as their regular home environment. The thing is though, is that even with all the GUI "easyness" of Ubuntu and its counterparts, there is still a huge reliance on the terminal which is why I stopped using it. There are also random things that don't work the way they should, so you need to fix them in terminal, and sometimes the fix could take you a couple hours just to figure out. I was personally having issues installing Java at one point and looked up every possible solution, each pertaining to the terminal with strange commands that, of course, didn't work. I even asked 2 of my expert Linux buddies and they had no idea.
So, I wouldn't advise moving from Windows/Mac to Linux, but if you're just putting it on that USB drive to use as a portable OS when you're on the move then it should do you fine.