Mathew Porter has a link to why Hibernate is successful  "Why This Project Is Successful", in stark contrast David Johnson has a blog on the motivations of the OJB project.  What I find extremely interesting is the markedly difference in style.  Hibernate says "do one thing well", "avoid over design" and "avoid standardism".  While OJB says "provide several personalities", "give developers a choice" and a "layered architecture shared by all three toplevel personalities".

So, this is a proving ground, a simple design that does one thing well versus an elegant design that does many things. 

I appreciate the elegance that OJB is trying to achieve, however, it isn't clear that developers are really going to need this. I like elegant design, I like good architecture, however in this instance by bets are on Hibernate to take the crown.