CouchDB implements a DB per user approach. Personally, I've found it much easier to use than an SQL DB for web apps I've made, but I've heard others who've always used SQL say they were frustrated with it.
It is nothing you cannot overcome with the right hacks (what can't be overcome with the right hacks?), but it is frustrating that the network-based API wasn't designed for high latency use from the start. It didn't need to use the exact same API that was designed for a low-latency environment, but that's what we got. As SQL and web apps typically means MySQL or Postgres, that means you are apt to encounter the API design problems.
Granted, it seems there is renewed interest in SQLite to move the SQL database back to the way it was designed to be used. Which isn't surprising as all things in computing come and go in cycles. Once we round out that cycle and get back to "database on the network", maybe we can get a more well designed API meant for high latency to remove those frustrations.