I've recently been looking into the SpringSource Application Platform (S2AP). This is an OSGI based app server, where instead of deploying applications jammed full of open source jar files, you can deploy apps that define dependencies on specific versions of jars (bundles) or libraries (grouped bundles). These versioned jars are held in a repository within the app server.
What is interesting from an Ivy point of view is that you can configure S2AP to look for its jars in an Ivy cache - yet another great use for Ivy.
I'd recommend having a look at S2AP - it's still in beta at the moment but deploying our app so that it uses OSGI bundles within an Ivy Cache rather than shipping them in a WAR reduced our WAR size from 50 megs to 52k !
There's a good blog entry about it here :
http://blog.springsource.com/main/2008/04/30/introducing-the-springsource-application-platform/
and information about how to configure it to use the Ivy cache is in section 6.5 of the user guide.
As S2AP is very OSGI based, the Spring guys have been busy converting many jars into OSGI versions. There is a really nice repository of them here:
http://www.springsource.com/repository/app/
which you can point a resolver at.