StarDestroyer.Net BBS

The project I'm working on has a lot of old, old legacy code and workarounds that occasionally drive me to distraction. In particular, metadata is stored as a sort of key-value interface in a relational database and users can generate documents that use a very broken templating system. I'm looking to replace this stuff at some point.

Does anyone have experience with K-V, document-oriented or other schemaless databases to handle this stuff?