The Java Content Repository spec and its open source Jackrabbit implementation were once my favorites (as a proof you can watch my ☞ interview about the InfoQ Architecture) and I continue to believe that they carry a lot of good promises.
Below you can find the presentation on JCR, “The Ultimate Content Store? JCR in 15 Minutes” by Bertrand Delacrétaz, one of the main Jackrabbit developers
Update: I have received an interesting comment on Twitter about JCR that I’d like to reproduce here in order to allow other readers to clarify it.
JCR is a well written specification. The problem is every impl. of its has sucked in terms of performance, integrity and scaling.