[sespindola]

In my experience, hosted database providers are almost always either cost or latency prohibitive.

Nowadays, in PostgreSQL is quite simple to replicate a db via log shipping[1]. You can even stream the WAL to an S3 bucket.

[1]: http://www.postgresql.org/docs/9.3/static/warm-standby.html

[threeseed]

I currently use MongoHQ and get response times in the tens of milliseconds for $18/month. Hardly cost or latency prohibitive. I've seen similar times for less money with Cloudant.

Making sure that master/slave scenario works when you need it to requires extensive testing and care. You also failed to address backups. I've yet to meet anyone who runs their own database who actually tests their backup.