The database space has for sometime been an active Open Source area, thanks primarily to MYSQL, Recently there is a lot more news about the space, Eweek is running a special report discussing the Opening of Databases to open source, Also below are links/excerpts from various posts on the Open Source Database space.

• Forrester has an report, titled open source databases coming of age, available at the MySQL Site. View image
• "Following in the footsteps of the Linux operating system, open-source databases are moving toward mainstream use and threatening proprietary software alternatives, according to a new survey. Open-source databases are in the experimentation phase of the market but will move to widespread acceptance by 2006"(Shankland 2004). Source
• Infoworld post titled Is Open Source Enterprise Ready? you cannot run an enterprise on open source DBs. They just aren't there yet. So far, none of the open source DBs can handle XML, nor can they do any kind of real BI whatsoever. Quite often, as is the case with MySQL , they don't even have a complete coding set. Ingres is the only one so far that I've seen that could compete with closed source, but that's only because they used to be closed, and now CA has opened it up. Open source simply doesn't have the development effort that closed source does. A group of guys in their garage can never match the money that closed source implementations have. Companies like Oracle, IBM, and MS put millions into their products every year, and that kind of funding will always be richer in features, and stability.
• Sadagopan BlogUpdate: barley I finished publishing this - News.com reported Few bugs in MySQL database - a source code analysis of the MySQL database, a popular open-source program at the heart of many Web sites, revealed few bugs compared with the number found in commercial code, as per testing company Coverity.Commercial code typically has anywhere from one to seven bugs per 1,000 lines of code, according to an April report from the National Cybersecurity Partnership's Working Group on the Software Lifecycle ,which cited an analysis of development methods by the Software Engineering Institute at Carnegie Mellon University. Coverity's analysis of MySQL found an average of one bug in every 4,000 lines of code--results that are at least four times better than is typical with commercial software. While this looks interesting, we still beleive that Opensource databse has a longway to go before being considered seriously for the enteprise.
• This is another link that I found which provides an comparison of the various open source databases.