This seems to be a pretty good implementation of FriendFeed's schema-less MySQL ( <a href="http://bret.appspot.com/entry/how-friendfeed-uses-mysql" rel="nofollow">http://bret.appspot.com/entry/how-friendfeed-uses-mysql</a> ) and this option would probably beat most of the simple key-value stores in terms of perfomance, backup and replication.<p>One should note thought that more modern NoSQL databases aren't only key-value stores. For example, Redis offers KEYS command which can scan the store by a pattern. Tokyo Tyrant (another "key-value" store) offers Lua scripting.
Neat - I just tried it. I am fairly much "in like" with both activerecord and datamapper, but Friendly is cool. I wonder how much work it would take to support PostgreSQL.<p>Friendly looks especially good in MySQL shops - otherwise I would suggest taking a good look at MongoDB (or Redis, CouchDB, Cassandra, etc.)