High data flow rates with iCloud?

I was trying to blog on a foreign trip with a hotel-provided user account which allowed for 500MB of data for $20. Seemed reasonable, as I wasn't expecting to go anywhere near that with the modest data needed for my mostly-text blog. So I signed on, and in about 20 minutes, I got a message saying I had exceeded my data limit! How could that be? I called the hotel techie, who asked if I was using iCloud. "Yes", I said. He said it was updating all the time, and had a tendancy to run up people's data allotments. It seemed unbelieveable, but i turned it off, after the techie gave me another free code to use. Sure enough, that brought the whole thing under control, and I was able to do what I'd wanted to do using only about 10MB of data. So what's up with iCloud? What should I turn off of the things it's syncing to avoid this phenomenon? Mail? Contacts? Calendars? All of the above?