For most, a generic off-the-shelf microSD card is probably just fine. It may slow things down and take a little longer to access, but that's alright in return for lower cost. For some people, though, having their device slowed down by a budget microSD card isn't an option. Other people need high performance for recording 3D and 1080p video. It's those two groups that the SanDisk Extreme Pro microSDHC UHS-I card is for.

^{I think SanDisk caught Sprint's case of diu nominibus.}

SanDisk touts the Extreme Pro as being "the fastest microSDHC memory card on the market." I haven't tested every card on the market, but they're probably right.