Works very well for me since I get five gigabytes per month for $50 ($10 per additional megabyte up to $80 at which point it is unlimited.) Two minuses compared to a 3G iPad.
() No GPS in the iPad but I don't really need it since my Android cell phone provides better GPS service including turn-by-turn voice navigation than the iPad.
() I don't have the option of turning off the data plan on a month-by-month basis as I could with a 3G iPad. But since I need to have access for at least a day or so via 3G or 4G, the incremental cost is something I'm willing to bear. And while there are many months that I could get by with the 2GIG plan (for $30), there are months in which I come close to the 5 GIGS and the difference is non-existent in those months.