Spotted on the cassandra users list. This was on EC2 large instances, which should put the wind up anyone who thinks you need specialised machinery for anything but extreme performance/scale tradeoff requirements. For many cases now, it seems you don't need to just pick one.
And check out Joe's startup, SimpleGeo: a scale out geo spatial/location platform running on (I think still) AWS and using Cassandra as the backing database, which a bunch of geospatial software built on top. It is a new world - a startup couldnt have done this even a few years ago, not without a boatload of VC funding for the hardware.