Just updated my world and both rails 2.3.10 and rack 1.2.1 were pulled in. This is not a working combination, and rails will refuse to load. rake version must be 1.1.0. Reproducible: Always
It looks like we'll need to slot rack 1.2, so that 1.1 and 1.2 can be installed side by side. I've tested this with Rails 2.3 and that seems to work fine. One caveat is that rack installs a binary in /usr/bin which can't be shared between the slot. We currently don't have a good solution to handle that. :-(
*** Bug 343579 has been marked as a duplicate of this bug. ***
I've masked rack-1.2.1 temporarily until the issues with it and Rails 3 have been solved.
This has now been fixed by putting rack 1.2.1 into a separate SLOT. /usr/bin/rackup is now only provided by rack 1.2.1, thus avoiding the conflict.