I’ve blogged a couple of times about the state of the Xalan-J project at Apache. Recently I’ve been using Ohloh.net to track some other projects, in particular the committer activity. For Xalan, here is a graph that displays the Commits since when the project was created at Apache.
Other stats, can be found on the Xalan entry on Ohloh.net. For users considering using an open source project, you may want to check out Ohloh.net, as it can give you an idea of the overall health of the project, and whether it is actively being maintained.