We do this with out landlord in a somewhat reverse situation. He has the router and we are on his network. We bounce it through our time machine to extend the range but I understand we are all on the same account. It's great and having the included internet brought our duplex into our price range when we initially moved in. I guess it comes down to how well you will know your neighbors. We've known ours for a few years so we didn't think anything of it. If you're going to constantly worry about it then decline from sharing so you don't have that added stress.
2009 Surly Cross Check
2003 Cannondale Bad Boy
Motobecane Nobly (60's or 70's)