We use stripes now on all our production sites, and have been for about a year now. It is an awesome product compared to struts, which we used to use before that. Just the fact that there are literally no XML config files and that you can set it all up with a minimal amount of classes and annotations is awesome.
In terms of scaling & speed it actually seems to be better than struts, and my guess would be because there are less layers involved. The code you end up with is a lot cleaner as well, because you don't have to go off to seperate XML files to find out where redirects are going.
We use it with an EJB3 backend, and the two seem to work really well together, because you can use your EJB POJO inside your actionBean object, without needing a form object like in struts.
In our evaluation we considered an alpha version of struts (that supported annotations) and a lot of other frameworks, but stripes won because of it's superior documentation, stability and clean-ness.
Couldn't figure out how to leave a comment: so to answer your second question we haven't encountered a single bug in Stripes that I know of. This is quite impressive for an open source framework. I haven't tried the latest version (1.5) yet, but 1.4.x is very stable.