MPG level 2 is 1 gig per hour at the lowest resolution (That is skipping every other pixel basically, When expanded you won't notice it but if you do not have the right CODEC on your viewer it comes out half width).
MPG Level 4 which is the current "Standard" is more economical But that said.. You can easily put an hour's video in a quarter Gig. I do not think I have any handy to look at just now for file size, but the bottom line is this:
You use a LOT of data. Here are some "Stats" for one hour internet TV show.
Episode 61 (High Def 1.55 GB)
Episode 61 (Large 575 MB - H.264 - MP4 - iPod) This is what I tink Netflix et-al use.
Episode 61 (Large 420 MB -Windows Media)
Episode 61 (Small 123 MB - Windows Media)
Episode 61 (AUDIO Podcast 66.9 MB MP3)