I'm at 175mb in just 5 days, phone is a couple of days off a month old, so I've already downloaded and updated everything I need.
For that 175mb the top offenders are browsers, play store, and maps.
From June 7th - June 30th I used 2.02gb, good thing I'm on an unlimited plan. I never got in the hang of waiting until I was on wifi to update stuff. But a large amount of data is consumed by surfing, for me.