1. YouTube uploads [I do it occasionally, a few times/week at most] Just can't wait to share that epic video of your friend wiping out on his skateboard? Or your totally legit Bigfoot sighting? Upload at your own risk: Depending on settings and various other factors, each minute of HD video you shot can be as large as 200MB. So if you upload just five 1-minute videos per month, that would eat a full gigabyte of your data allotment. Wait till there's Wi-Fi!
2. Video chats [once or twice a year with DW just to amuse her] Stop the Skyping! And the FaceTiming. And all the other video calling -- if you want to save data. Though the rate of consumption varies depending on the app you use and resolution of your chat, a Jetsons-style phone call can cost you up to 3MB per minute.
3. Online gaming [never so far, on that little screen?] Don't worry, Trivia Crack addicts, turn-based games like this and Words With Friends aren't heavy data-users. However, real-time action games like Asphalt 8 and Modern Combat 5: Blackout are a different story, with some estimates pegging their data use at 1MB per minute of play.
4. Music streaming [I do Pandora a few times/year, but my iTunes library is on my iPad] It's so easy (and awesome) to plug into Pandora or Spotify when you're, say, riding the train home from work, you might not realize what it's doing to your data plan. What it's doing is killing your cap. If a music service streams at a 320Kbps bit rate, that's 2.4MB of data per minute, or a whopping 115MB per hour. Even if you tune in only a couple times per week, it's easy to rack up big data numbers. Fortunately, a lot of mobile apps let you downshift to a lower bit rate, a very advisable move if you must listen on the go. Pandora, it's worth noting, never streams at more than 64Kbps on mobile devices, even if you're a Pandora One subscriber. One other option: if your music service allows it (and most do nowadays), download your tunes (via Wi-Fi, of course) for offline listening.
5. Video streaming [never yet] If music streaming is bad, video trumps it by an order of magnitude. Awesome though it may be to binge on episodes of "Black Mirror" or trending YouTube vids when you're on the treadmill at the gym, streaming can swallow as much as 50MB per minute.