There are/ have been legions of two piece groups doing all manner of different stuff, lightning bolt, guapo, pink and brown, hella, the spinanes, swearing at motorists, and the white stripes spring to mind immediately (at two ends of the spectrum. My friends the blood red shoes
www.myspace.com/bloodredshoes
are a two piece.. the guitarist in that just relies on turning up and using the deep switch on her marshall head. I can't say i notice the lack of bass. I play in a guitar and drum two piece and I'm still looking for a good way of getting the low end, at the moment I'm using an ampeg B15T and a vox cambridge.. but getting a bit too much hum, I've also just tried using the speaker of the B15 as an extension cab for the vox which actually works really well. Looping is all very well but requires a really tight drummer (and for the loop maker to be super tight too), most people I've seen using loopers well tend to use them in a more ambient wash type way.. I've tried using an akai headrush to lay down loops in a full band before and it was very difficult to use for melodic type parts, possibly down to my incompetence more than anything else though.