I've upgraded Mongo Mapper to 0.9.1 to take advantage of it's Rails 3 integration, and it works with Devise 1.3.4 which removes the deprecation warnings.
To do this, I had to pull down the devise-mongo_mapper plugin to avoid version conflicts - it works with the newer code with no changes.
Mongo Mapper 0.9.x has a new configuration hookup that I had already written myself, so that code had to get a small change.
Joint, a Mongo Mapper plugin, doesn't work. I was going to replace Joint anyway for my own needs, now I need to do it today instead of next week.
Now I'm 2 hours in, and still not working on the Asset pipeline work I want to do, but my app is running except for the Joint bits
My next step is to fixup my morass of CSS and JS files to use the Asset pipeline correctly. That's probably another hour or so.