When svnmerge.py inevitably yaks all over yet another branch we're trying to merge to a release candidate after a rebase or two, I'm only barely capable of figuring out how it got confused and how best to recover, and the rest of my team (experienced developers all) isn't even as good at it as I am. I hear 1.5 with merge tracking isn't that much better.

svn is an extremely leaky abstraction, and just not a reliable enough tool to unleash on the people you're describing. Fortunately we're switching Real Soon Now(tm).