I'm getting ready to set up an LJ server, but have no interest in MySQL. Yes, I've seen the dev FAQ that attempts to justify why it's being used over PostgreSQL, but the fact is that MySQL doesn't behave in a manner consistent with SQL standards.
That said, I'm shooting to tweak LJ into being a little more DB agnostic...in my case, I'm setting it up for DB2, Informix and Cloudscape. A couple of reasons for this...I want to use those products' extensibility to beef up searching functionality, add portability and spatially-enable things so it's easier to visualize where everyone's located (more automated than LJ currently can handle).
Anyway, my point--has anyone else done this before? I'm going to direct this question to lj_dev as well, but I'd rather just bring them a finished product to do whatever they will with...