According to my provider, I've used 6.8MB of data within 3 days.
The thing is, I don't know how. I've installed DroidWall and WiSync and only used Waze (a navigation app). I installed Traffic Monitor which shows Waze using less than 800KB and other apps even less (some of them used traffic before I setup DroidWall)
Any clues as to what is using 6MB??