I'm always on the lookout for different ways of doing the things I'm familiar with. Once in a while, I learn a better way of doing things. Even if I don't, I find that it helps me realize what I like and dislike about the techniques that I'm used to.
Take creating web applications for example. I'm familiar with JSF, both with and without Seam. Overall, I would say that I agree with the ideas behind JSF, but in practice it is not easy to be productive in developing a medium to large sized web app. It seems like some things that should be very easy to do are difficult, but maybe that's just me. Seam adds a bit more complexity, but helps overall. To the JSF world of managed beans, Seam adds ways to manage the rest of your objects called scopes. This is a good idea on paper, but feels a bit like using global variables (albeit with managed lifecycles).
So I decided to give Wicket a try. What stood out to me right away is the simplicity of it. There's very little configuration, and no XML other than web.xml (which makes me realize how much I dislike having stuff like page navigation in an XML file). Each page template corresponds to one Java class. Also, there is no EL or OGNL so your markup is sure to have no logic whatsoever, which is great for those of us who prefer to code in Java. That's the bottom-line benefit that I see with Wicket: everything happens in Java code. Which means you get all of the benefits of writing Java code in an IDE from debugging to refactoring, etc. I haven't tried it, but I've read that it's easy to use alternative JVM languages such as Scala and Groovy instead, if you are so inclined.
Wicket is very friendly to the web designer because it does not invade the markup, so the designer can see what they are getting without firing up a web container. For now, I haven't seen any Wicket components which look good "out of the box" (translation: you probably need a web designer). However, there is no reason why there couldn't be such component libraries for Wicket. That will come with increased adoption, if it happens. After all, creating a component library in Wicket means putting your classes and markup in a JAR file, so it couldn't be easier.
Some minor gripes I have with Wicket are that the markup has to stay in sync with your Java class (but all web frameworks I have used also have this problem), it can sometimes add junk to your URLs after a form submit (maybe there's a way around that). Also, there's quite a bit of casting when using version 1.3, but they are adding generics to version 1.4 which should minimize that. Overall, I'm very impressed.