I find this statement grossly underestimated:
Sitting and watching a few YouTube videos everyday will push you way over that.
Actually, I was surprised how little I use. I tethered my iPad to my Android phone and used it for four hours while I waited on Black Friday lines. I watched an hour-long TV show on Netflix, did lots of browsing and IMing, and found I used... 250MB. I thought I would at least use a gig.