Question: What system do you recommend for implementing "automatic updates" for some java (desktop) application? I'd also want to have module/plugin installation and update. Think Eclipse and Firefox.

I'm aware of Eclipse RCP's OSGi stuff, and also NetBeans RCP has something here. Do one have to buy wholly into their respective RCP stuff to use their module and automatic update systems?

Are there other options?

Answer: 
I believe install4J now offers this functionality as part of their install builder (<http://www.ej-technologies.com/products/install4j/overview.html>) We've been wanting to check it out but haven't had a chance yet.
Take a look at [Equinox p2](http://wiki.eclipse.org/Equinox_p2), which is probably what you meant by "Eclipse RCP's OSGi stuff"... AFAIK you *will* need to OSGi-ify your app to use p2 (which at the very least means making your whole application one big bundle).