I have to say the issues with getting Dungeon Defenders to work under stock Ubuntu 12.04 will make me reconsider ever doing a Humble Bundle again. It now "launches" for me, but I'd be hard pressed to say it "runs" (crawls maybe). There should be some compatibility checking before allowing a game to be included.
I assume there is an under-the-hood way to get FPS? I'd be happy to post.
I've got it at smallest resolution, and it feels like "a pig on iceskates".. ie. slow-ish and seems like I overshoot what I want. I3-2100 and GT440 gpu. Not top of the line, but able to handle the other linux games I've thrown at it (going to check out the Steam beta when I have the time).