Howzit people!
RompelStompel ... interesting question you've got there .... make sure that you've got programs like "Spybot" and "AdAware" running, to check for spyware etc on your PC ...
I had spyware "hidden" on my PC, that munched up 3 - 4k /sec everytime I logged on ...
That would've caused about 10Mb of data within 1 hour!
After running Spybot and AdAware, they were quickly removed, and since then, I've got a "QUIET" link, when I'm not browsing or doing anything specific

Running "Zone Alarm" firewall also makes the connection MUCH more safer. (interesting to see how many PC's on the 3G network, tries to connect to my PC on port 445 ! not good at all!)...
For anyone else reading this ...I've got a similar kind of question ....
When I'm connected, my VMC, Net Limiter, and right clicking on the "connection" icon in Wndows, all show me 3 different data usage counts!??
So witch one must I believe??