I installed DB2 Express-C on my Ubuntu box, and not only did it break itself after one day, it completely broke apt-get. I've never had that experience with any other software on Ubuntu. I tried going through internal channels and no one could point me in the right direction. I doubt that external channels would be anymore responsive.<p>DB2 deviates from other databases I've used with respect to syntax. Most free information is only from IBM. Compare that to how much information there is about MySQL.<p>pureXML is not amazingly fast. IIRC, it was orders of magnitude slower than relational queries. I believe development on pureXML was recently canceled.<p>Occasionally, we run into limitations of MySQL. When that happens, it usually means we're attacking the problem incorrectly. It doesn't mean we need a faster database.<p>I would be most interested to see examples of startups that use DB2 Express-C; I've not heard of any. When Facebook built one of the largest data systems around with MySQL+memcache and other open source software, it makes you wonder why you need "enterprise" solutions.<p>EDIT: disclaimer: I used to work as a developer on DB2.