Jonathan Schwartz (Sun Microsystem CEO) has reassured people like me in his latest blog post: after having bought MySQL, they apparently stay committed to PostgreSQL as well

What happens to your commitment to PostgreSQL?

It grows. The day before we announced the acquisition, and within an hour of signing the deal, I put a call into Josh Berkus, who leads our work with Postgres inside of Sun. I wanted to be as clear as I could: this transaction increases our investment in open source, and in open source databases. And increases our commitment to Postgres - and the database industry broadly. The same goes for our work with Apache Derby, and our JavaDB.

Josh says it exactly right on his blog - Sun wants to be the leading provider of datacenters. Not just MySQL datacenters. Exactly.