Apache Jackrabbit was just released in version 1.5.
It looks that this is the "yes, we heard you" release, and is a huge jump forward for straightforward usage:
1) grab the jar-file
2) java -jar jackrabbit-....jar
And... there is no step 3 :).
I can't stress out enough the importance of such easy usage. While it already has been more or less simple to use Jackrabbit in, say, semi-professional setups, it now has the chance to hit the Main Street. "Want webdav? Well, you'd better use that jackrabbit thingie".
Ok, there may be some steps 3, but I will write about those later