Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I have a wifi ipad, I was very surprised how long it takes to download a HD movie even over good internet (which I wasn't always at.) The good thing is that the ipad remembers where it was when downloading, so I could walk out of range, and it would find where it left off in the download when I got to another network (and told it to resume.)
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.