MyOpinion
I've recently been seeing a lot around about MySQL as a possible replacement for commercial databases. A comparison of features between MySQL and SQL Server (the database that I'm most familiar with) shows that they are pretty close in most of the things that I care about. The fact that it is used on the quite excellent U.S. Census Bureau website makes it even more appealing.
When I get some time to investigate, I'm going to try to learn more and maybe build a few things using it. One thing I'm not too fond of is the name - it is a little silly. Why not something a little bit more like Apache?