IPAD APP internet usage

Notifications, checking email, and web surfing use very little bandwidth. Those activities hardly register on a basic 2GB limit 3G plan.

Streaming audio, like Pandora, actually uses a lot less bandwidth than I thought as well. People on 3G plans have told me that they're no where near reaching their monthly bandwidth cap even when playing music for hours every day.

Movies are the bigger bandwidth hogs, and a few Netflix, ABC TV shows, etc a day will take you over your limit if you're not careful.

You didn't mention the MiFi plan you have, so I'm not sure what kind of limit you have.