Bruce Perens (now a VP with Sourcelabs) has blogged a sharp little analysis of Oracle's buying spree whose short form might be Bobby McFerrin's "Don't Worry, Be Happy."
Or we can go all Madonna on Larry Ellison's troops and sing from the top of the balcony:
"Don't cry for me, oh mySQL. The truth is that Oracle can't have you. Through open source's wild days, its mad existance, it keeps its promise, so keep your distance."
OK. Andrew Lloyd Webber I'm not. But Perens' point is pretty simple. Never mind that Oracle bought InnoDB, a transactional back-end to mySQL. It's still open source, it still works, and mySQL doesn't have to build a new one unless it wants to. The same is true for Sleepycat, a SQL-less database for embedded applications. So long as the license remains open source (and it does), no problem.
What Oracle is buying are some of the people who can extend and support these products, not the products themselves. Even when a product goes closed-source (as Nessus did last year) that's just for the new version. You can still use the old version, you can still extend it with a fork.

Perens' last line is really his lead. "Open Source developers smile as proprietary software companies fight each other by collaborating more."I couldn't have said it better myself. And neither could Webber.