My phone logs how long the data calls are, but not the amount of data used. I just checked my account and I have used 20MBs of data 2 weeks into the billing cycle. A large chunk of it though appears to be from using Cingular Video one afternoon when I was bored. The rest of the log looks like its about 200k-1.5MBs each use. My use is similar to yours - Google, Wikipedia, gadget sites, news, and of course this site. I'm guessing even with heavy usage it would be hard to exceed 100MBs/month.