Open source databases still have a very long way to catch up to Oracle. I was at Oracle Open World touring the exhibits on Tuesday. Just for fun I asked everyone I met whether they used open source databases or saw demand for them in their businesses. The answer almost universally went like this: "No."
One simple reason explains much of the Oracle dominance as well as the inertia of many companies in switching to something else. A huge number of enterprise applications like Siebel or SAP run on Oracle. MySQL and PostgreSQL applications on the other hand are either custom code or belong to an area where open source is truly dominant, such as web site content management. Even when more applications run on open source, most companies will adopt them as supplements to existing systems, not as wholesale replacements. Oracle and other commercial databases will continue to rule enterprises for a very long time.
A lot of the focus in open source database development is on matching capabilities of commercial databases. What many open source users really need is the ability to integrate. That in turn depends on features like heterogeneous replication as well as bulk loading. These are not on the road maps of most open source database projects. However, they will be one of the factors that eventually enables open source to break out into a much bigger arena.