If the Droid's "unlimited" data plan from Verizon is only 5 GB a month, how much data do people usually use?

I read today on Slashdot that the Droid's "unlimited" data plan is actually only 5 GB a month. I'm wondering, based on other Android phone users' experience, what's the average data usage per month? Average monthly iPhone data usage would also be handy.

Also, is there a good tool for seeing this data on a monthly basis? On the iPhone, going to Settings -> General -> Usage gives you the amount of usage since the last Statistics Reset. That works if, for example, you're going on an international trip, and remember to reset statistics before you go so you can watch when you hit the international data roaming limit, but it's a bit tedious to do more often.

And there's some data on my ATT online bill, but in typical telco fashion, quite hard to decipher. Wondering if there's a simple app for collecting this data and setting alerts when you're near the limit.

But in the short term, a few real world answers of the form "I typically use n GB a month" would be helpful.