I'm using a 100mb partition for /boot on a clean install of Ubuntu 13.04. With only 2 kernels on it, it's already full. The biggest culprit seem to be both initrd (18.104.22.168, 22.214.171.124) images are around 32mb each (and a 22mb /boot/grub/unicode.pf2). I've used this same partition with an older install of 12.04 and I never had any problems with having multiple kernels. In fact, I had a whole ton of them.
While looking this stuff up, I've seen mention that it may be related to nVidia drivers. This would make sense because I encountered the "/boot has no space" error when trying to change my nVidia driver for the second time since the clean install.
Any thoughts on what I should do here? It would be a real pain in the butt if I could only keep 2 kernels at any one time.