The generator only drags when engaged (like when you flip it down when you want the lights to turn on), and I have heard most people don't notice much difference. I have a AXA HR bottle generator in my possession and have the intention of putting it on one of my bikes... as for ruining tires, I think it depends on the tire and where you put it. Your fat franks have a generator strip-- it is thick rubber there with ridges to help grip on the little wheel. Might be worth considering...

One reason I have considered running one, is inspiration from one of Velouria's blog posts about the matter:

http://lovelybike.blogspot.com/2010/...or-bottle.html