Re: Multi-Instrumental people
I actually just came to drums last fall from dabbling in guitar for like 10 years. Never had a lesson, just picked up a lot of stuff along the way (my college roommate was a sick guitar player, and my best friend is now becoming a very capable player--hence my switch to drums). I have a really basic understanding of root notes, scales and modes--just enough so if like an E power chord is being played, I know where to start playing some VERY basic lead noodling. My left hand is pretty clunky and uncoordinated, but I can dish out some pretty chunky palm muting (metal has always been my thing). I guess I can play bass a little bit (root notes--every guitar player should be able to play at least a little bass by default).
It really helps knowing my way around guitar. I can write riffs, so then my friend can play them and build on them while I play the drums. It's easier to say, "Hey, start with that open E-string palm-muted tremolo riff" than "Hey, do that weird chunky thing you were doing earlier that's kind of fast."
I also have recorded some really basic but many-layered and spacy (read: AWESOME--to me anyway) Ray Lynch/Enigma-style stuff directly onto my wife's Yamaha keyboard. It SUCKS because it has since deleted itself. I'll never remember all the stuff I did for those :(