I don't know the characteristics of bikesheddb's upstream in detail (if there's ever a production-quality release of bikesheddb I'll take another look), but in general using something that can scale horizontally (like Cassandra or Riak, or even - for all its downsides - MongoDB) is a great approach - I guess it's a question of terminology whether you call that "sharding" or not. Personally I prefer that kind of datastore over an SQL database.