I"m an extremely heavy user, I stream not only music but also movies from my servers at home, TV, from Tv.com, Hulu and such, and am almost always over 2gb, and usually close to 4-5 gb.
If you're only surfing the net and streaming mostly audio I wouldn't be worried about it, but if you stream a lot of video it might be a cause for concern.
I have the old unlimited plan, so it's not a concern for me. YMMV.
