At one point, we had to enable RIP on a 4900 to get it to route between VLANs. No, we don't know why. Enable RIP and it works; disable RIP and it stops routing (send packets to the default route instead).Stupid.
This is a collection of techical information, much of it learned the hard way. Consider it a lab book or a /info directory. I doubt much of it will be of use to anyone else.