I'm pretty sure there is a subscription fee. I think I heard about it either on Steam or the official website. I'm gonna check it out a second time.I think you heard about the subscription from the voices in your head because, as a completely sane person, I can say that there are no subscription fees attached to Borderlands.
:EDIT: Hmmm, guess not. Must have been some other game that is coming out in 2009. Still, I'll wait till a friend gets it to see how good it is. It looks like Mass Effect + Fallout 3.