I'm already a firm believer in the iPad 3G and its no-contract data plans, but AT&T's released the nitty gritty details, in case you wanted to check the fine print. Pretty much the same, but a few new bits.
For instance—and a big thing if you're trying to stretch out the $15/month 250MB plan—is that while an iPad 3G data plan is active, you have free access to all of AT&T's Wi-Fi hotspots. (Of course, this helps them too by reducing strain on the network.) And, happily, it's pretty clear about showing how much data you have left every month, with alerts at 20 percent, 10 percent, and you're-out-of-data-dammit. When you run out, you have a few options: add another 250MB or go to unlimited, which starts a new 30-day cycle. (Or you're just out of data.)
Also, the plans do automatically renew every 30 days, and the countdown begins the second you confirm your data purchase on the iPad. So if you want to cancel and truly go ad hoc, it'll take a bit of attention. But really, this is the best kind of data situation we could've hoped for. I'm just praying it'll be usable in NY. [AT&T (PDF)]