How far can you go with the iPad's $15 data plan?

We turn off Wi-Fi to find out if you can get away using AT&T's cheaper, 250MB iPad data plan instead of the $30 unlimited plan

If anything is revolutionary about the iPad, it's that Apple persuaded AT&T to do away with the standard lengthy contracts for cellular service in exchange for a month-to-month commitment. Equally impressive, Apple also managed to wrangle a cheaper data plan out of AT&T, still sans contract: $15 for 250MB of monthly data. But on the iPad Wi-Fi + 3G, a device with a powerful Web browser, a hot App Store, a YouTube app, and more, how much will 250MB actually get you?

I signed up for the $15 plan over the weekend and used my iPad as I normally would, with the exception of leaving Wi-Fi off to see how far 250MB could really go.

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What I used
In a typical day, I use Safari to visit Tumblr, Facebook, and do a few Google searches. One day I shopped for an iPad GelaSkin; another I used the iPad version of Articles to look up two Wikipedia entries. I usually start NewsRack, my RSS reader of choice, two or three times a day to read the latest news over lunch or on the train. I have three accounts in Mail: One is push (MobileMe), the other two pull new messages once every hour. While I get anywhere from 30 to 80 or more messages a day, most aren't anything more than text, and a good portion are filtered away from my inbox by my Mac. I watched a few YouTube videos, and updated a few small apps -- between 5MB and 10MB apiece -- and that was generally about it.