This is my usage exactly. I won't rent through Sony because they impose a 24 hour period - I rarely have two consecutive hours to spend watching a movie any given day. Amazon uses a 48 hour period, which I can live with.
It's very easy to get the movies on my xbox, they cost about half as much as they would on itunes to rent, and they have a much better selection of movies I can see than Netflix since I can rent the ones I'm actually interested in seeing.