There's one non-obvious drawback to renting-- if you want a non-average car (say, an SUV), there may not be one available.
This is a good point, and it's worth noting that even making a reservation in advance might not guarantee what you want. When I was moving, Hertz accidentally rented the van my father and I reserved in advance to someone else. Ultimately they gave us a similar van and there were no major issues, but this still left me feeling uneasy.
I imagine that renting via a different service like Zipcar wouldn't have this issue, though I haven't used Zipcar yet.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.