I always had a difficult relationship with Wicket. It does have its strong points for sure, but building the component tree twice (once in HTML, once in Java, and keep those in sync) just doesn't fly with me. The URLs can become quite ugly as well, with lots of colons and WicketIds in them. Performance is okay and basically on par with JSF 2 (JSF 2 is a bit faster and uses less memory, but the differences are not that big)
One of the major shortcommings of Wicket is its community, n the sense that its simply not really there. Sure, the core developers are present and such, but relatively few people use Wicket making it hard to find anyone to answer your questions, writing a blog post or posting some example code.