jQuery is a pleasure to use. It's just plain useful. If you need to manipulate the DOM in legacy IE, nothing compares. I'm reading a lot of complaints about the overhead for legacy IE support (presumably from people with better clients than mine...) but I'm surprised no one has mentioned Zepto. I haven't had a chance to use it yet, but isn't it just a stand in for jQuery where legacy support gets stripped out? I'd love to see the benchmarks.