I don't own an N9, but from my short use I know the following at least:

exchange activesync (built-in, with calendar sync) - check
use of front-facing camera - check
skype - check
free ram - why would one need/want this on Maemo?

And N9, like N900, should not have excessive data usage. There are no background 'system' processes that use up data. All data consumption is from applications YOU are running yourself