On average, I use about 1.5GB a month. Less if I have more work hours, more if I am traveling. Even then, I never reach more than 3GB a month. Of course, I don't stream music on the go. And then again, my target is not to spend more than $20 - $30 a month on wireless bill.
Although I am glad that people are using more bandwidth (thus putting pressure on carriers to provide more reasonable usage quotas in this modern age), I don't understand why people are so willingly to give their hard earned money to the carriers. It allows the carriers to barely provide reasonable quotas. Seriously, the price per GB on average from carriers worldwide is not any better (arguably even worse) than what we had years ago. You would think wireless will be more affordable, but no. Even countries that used to provide generous quotas are not following the minimal quota ala North-American carriers (eg. Singapore carriers used to give 5 - 15GB standard, but now they are only doing 1-2GB standard, with the lowest tier going even lower into the megabytes, which is pathetic in today's usage). Yet prices are still the same or more expensive.