This week the GAS bug has bitten me, though its not for the usual stuff. This time I want a bass. One of these in Fullerton red with a tort guard, to be precise (that's almost a pun...)

I've been wanting to learn to play bass properly (ie not like a guitar player with a bass in his hands) for ages now. The thing that sparked this bass GAS was watching the excellent documentary "Standing in the Shadows of Motown". If you haven't seen it then, its about the band that played on virtually EVERY Motown single in the '60s and beyond. There's a reasonably length section in it about James Jamerson, the guy responsible for some of the best bass lines ever put to tape, that inspired me. Know any other "must see" music documentaries?
How many of you guitarists double on bass (another near pun...)? Any of you the other way around - bass players fudging it on guitar? And for those of you playing bass, what amps are you using? I intend to use my all tube 100W '70s Fender Twin clone while I'm getting started, I've tested it with a baritone thats lying around here and it sounds mighty! Anything I should be careful of, bar blowing/burning out the speakers (they're individually rated for 100W and are full range PA speakers anyway)?