O'RLY...
for the meme retarded: http://www.google.com/images?q=O'RLY

I've used firebird on a POS system I was developing. I've used the embeded version and the server classic version and they work very well. As a matter of fact I learned SQL from firebird. The syntax just works every where else. Very compliant!. You will not find auto indexers, but you can create your own with triggers. In my option, firebird can be used to replace most databases with little work.