I have Google+ instant upload activated and Galley is set to sync over Wifi. I rarely see Gallery high on my data usage list.
However, what I do see is something called "Android Media Server", and that averages around 200MB a month.
What's even weirder is that the list names change. I just went in and checked and "Android Media Server" isn't even listed anymore, but YouTube is listed at 210MB.
Even worse, although the total data used is pretty close to Verizon's widget, if I add up the individual amounts for each app, they never add up to the total. For example, Rhapsody is always under reported. It's saying I used only 63.58MB, but I know for a fact that the total number went up by several hundred during a recent long road trip. So there is an issue with the accuracy of the usage by individual apps.