Using Multiband Compression on drums (before the mastering)

Anyone do this? How does it differ to using a regular compressor on drums?

Occasionaly. It allows you to controll the dynamics of specific frequencies. I tend to use it mostly during the mastering process though.

It depends what you want to do to your drums. You can think of multi band compression as filtering your audio into four bands, Lows, Low-Mids, High-Mids and Highs(the cross over freq. of these is usually settable(is that a word?!?) in the compressor itself. Then put a regular compressor on each of these bands. It's just a way to compress different frequency ranges independantly in a full bandwidth signal. This is why it's mostly used in mastering.
In practice you should generally treat it like an EQ because it's really easy to kill the dynamics of a track with it.