I'm using Subversion for Leonardo and have recently started using Roundup for issue tracking.
I'd like to have some level of integration between the two. The sort of thing I was initially thinking of was being able to associate an issue with a revision and vice versa.
The Roundup wiki gives an example of making something like Version:37 in a issue message automatically get turned into a link to the version control system (or something like ViewCVS).
Because Roundup is extensible in the object types it manages, one could presumably go a step further and have a class called "change" and extend subversion to, every time a commit is done, create a new change object for it in Roundup including the commit message.
References to issues could then be made in commit messages (and the link automatically made). Furthermore, Roundup would facilitate chatting about revisions. Revisions could be classified by topic, assigned to people for review, etc.