We got an email from Rogers saying that we'd gone over our 60GB limit. That's not normal or even close to normal for us. We noticed that there was no high usage while we were away, but started up when we got home from our trip. Some detective work and we knew it was my machine and further sleuthing pointed the finger at GARMIN!!!! It was sending 11 GB a day to my machine of something into the ether using "Core Update Service". This is part of the Garmin Express program which is used for updating maps on the automotive GPS (nuvi in our case).
Beware if you run Garmin Express and your internet usage goes crazy.