They're great live. And not only do they put on a good show musically, but also an amazing performace visually. They're very fun. I wont spoil any of it for you, but they put on a very creative and high energy stage show. If you like their albums, particularly Yoshimi and Soft Bulletin, I cant recommend enough that you go see them.
Saw 'em last year with Beck, and for a bunch of "old" guys, they put on one of the most energetic, fun, and surreal shows I've ever seen. I literally had a smile on my face for their whole set, and I was totally sober. They sang me "Happy Birthday", too--which was cool.