I've personally been in between the 500MB-1,000MB/mo range in the past year. I don't tether or anything, but do stream internet radio over it, and sometimes internet video's (e.g., TED).

If you're only using the basic built-in apps, like email, web, and maps, and you buy all Apps over your Cable/DSL line at home and install via iTunes, you'll probably not go above 500MB.

But once you throw multi-media into the mix, and buying apps over the wire, it's a different story. 500MB becomes quite tiny.

I fully agree on this point, I've been on the 500mb plan for over 6 months now and I never past 500mb. Sure now there's supposed to be tethering, but that's a hole different story.