Femtocells make sense if you want better service at a specific location and are willing to kick in some money to make it happen. I did this myself at home, since we live somewhat off the beaten path. The problem comes up when your ISP starts limiting the amount of data you are allowed. This is the point where people (myself included) will have to reevaluate whether or not it makes sense. At a minimum if/when that happens I will shut down my cell site to traffic except for my family. I am willing to be generous to my neighbors only as long as I am not incurring additional costs as a result.
Bill Schweber, I believe you meant to say, "but we'll avoid those perspectives here." Another hazard of living in the days of the spellchecker: the perfectly good word but the wrong word. I suppose we will soon have grammarcheckers if they are not already available, and this problem will disappear, or more likely morph into some new problem we haven't thought of yet.
I, for one, would be willing to give up some of my cable Internet bandwidth to have more services and better cell phone coverage in my home. Not that it's really a problem now that I switched from Cingular (AT&T now) to Verizon. Used to be there were no bars on the phone indoors on the first floor, but it worked OK upstairs and outside. Now, the Verizon service is pretty much everywhere except in the screen rooms at work!
As far as billing goes, I'd want the guy parked in front of my house downloading movies at least paying for some of my Internet backhaul bandwidth. I don't see the service providers having a really hard time figuring out how to bill for it; they've never had a problem before. If there are dollars in it, somebody will find a way to extract them.