Not many. I and many others have posted the (very simple) math.
For ease of understanding, let's say a movie is 1GB.
1GB/day = 30-31GB in one month.
Actually a movie downloaded from XBL or Itunes or Amazon or PSN usually runs closer to 2 GB and if you want a 720P HD verison it's about 6 GB per movie.
whating 2 hours of Hulu a day at their LOW resolution is about 20 GB a month.
