I've just did testing this week.
First off, let me explain:
I live from monday to thursday in another town (college), then from thursday evening to monday morning I'm at my home.
Since at other town I use USB internet where I have 5gb month cap (getting wireless card soon, then will have unlimited), I had to check how much does Guild Wars takes.
1. I transferred from my old PC to new PC whoole guild wars directory so I didn't need to download anything.
In 1 hour my GW downloads aproxx 4,5-8,0 mb (never really seen it goes more then 6mb, but oh well).
Mostly I spend my time in Kamadan (decided to sell some things), and in areas VQ/mapping
Hope that helped.