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30 MB per hour is about right. Check out this post at Tested. According to the post, Pandora uses a 64 Kbps bit rate, which translates to about 27.5 MB per hour (not accounting for the overhead of the transmission protocols).
I reset my data counter on my phone and ran Pandora. On the low quality audio setting it used about 40mb an hour.on the high quality audio setting,it used about 60mb. Hope this helps answer all the guessing going on.