Looking at Blojsom
Blojsom is very easy to install and get running, since it's file-backed by default. I got an instance running in my JBoss (well, Tomcat was only needed) instance in about 20 minutes.
I don't much care for the file-backed storage though. It just feels like a scalability/synchronization problem. All the storage backend is abstracted behind a fetcher inteface, though, so I could really be tempted to create a fetcher to get data from the EJBs that run my current weblog.
As I've said in the past, I'd start working to extend these other blog packages, if I wasn't using mine to learn all these technologies. I could, on the other hand, start using Blojsom or Roller for my weblog, and pick up another project to learn Struts.