I just took a couple of these for a quick spin so that I could have an answer if anybody asks about them tomorrow (I'm doing a LISA'13 talk about cloud storage performance). They really are pretty zippy. Basically they seem about 3x as fast as their predecessors, particularly with respect to disk I/O. The 1GB type is among the fastest in that category at over 15K (synchronous random 4KB) IOPS, for only 50% more per month than competitors. The 15GB type got over 28K IOPS, which is among the best I've seen in a public cloud (e.g. Storm on Demand 12GB or the astronomically priced AWS hi1.4xlarge).

Network-wise, I got the usual Rackspace throttling-induced asymmetry - 194Mb/s going from the 1GB instance to the 15GB, 874Mb/s the other way. Likewise, the cloud block storage significantly underperformed the instance storage at just under 8K IOPS - though that's still really nothing to sneeze at in a public cloud.

For something you can rent by the hour these are pretty sweet. It's not too hard to find 10KIOPS-capable machines elsewhere for much less, but then again those IOPS might not do you much good if the machines are network-constrained (and many of the cheaper providers do tend to be). As always, measure for yourself. It's always good to see that bar being raised.