True, it's no Cassandra :)

Anyway I think 10gb per domain is reasonable for many people, but it is another limit of the store that could cause problems. Fortunately Amazon knows the boundaries of SDB, so it can put these in place and help inform decisions about using it for, say, a project that will need more than 10gb per domain, or more than 100 domains.

FYI, with a 1k limit per item this translates into approx 10.5M items per domain max. That's a pretty big data set to have capacity for without having to shard across domains out of the box at unlimited read/write scalability.