&#62;I believe development on pureXML was recently canceled.
Where do you get information like that? Nothing could be further from the truth.
&#62;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>Well, you start with understanding the needs of the application. Facebook and your neighbourhood bank have vastly different needs. When half of your friends see a post on the wall and the others don't for a few minutes nobody gets unhappy or even notices it. Ever wanted to deal with the bank which withdraws money from one account but does not deposit it in to another for a few days?
MySQL is a fine database for many applications but just because it is used by Facebook or Yahoo does not make it the right fit for every application. Just because DB2 is used by  every fortune 1000 does not make it the right fir for Yahoo either.
MySQL is typically not a great fit when you need to scale transactional workloads. Most people don't attempt to run MySQL on anything larger than a 4-processor machine and opt for horizontal scalability based on Master-Slave replication. Can be a solution when slaves falling behind the master is not an issue (e.g Facebook) but will not work very well if you need transactional integrity for your data.  Can MySQL be made to scale on larger machines? Yes, if you are Google you can and they will be contributing their bits to v5.4 of MySQL. For the rest of us who need to do enterprise apps it si quite a bit easier to pick a DBMS that does it already and has proven itself. That means DB2, Oracle etc.