I mostly use Oracle and sometimes SQL Server. I used MySQL about 2 years ago quite a bit, but never really got into it. My skills have grown since then and I installed MySQL 4.0.x on my system for kicks. Once I got into the command line mode and started hacking around in my mysql table I couldn't get enough. The fact it's free, has an amazing admin tool in development, and how easy it is to get up and running just blows me away. Great stuff.