While I remain committed to SQL Server, after a lengthy evaluation and feature analysis process, we will start advocating MySQL 5 to some clients under a set number of conditions, both on the Windows and the Linux platforms. While MySQL was previously lacking some critical foundational features, v5 ups the ante considerably, filling a particular niche in the solution spectrum. This is a part of a wider trend at yafla of embracing some of the "alternative" platforms, outside of our normal Microsoft-enabled comfort zone, where it benefits our customers and the solution.
Due to licensing conditions we still won't be targeting our applications at MySQL.
We still advocate PostgreSQL, another excellent open source RDBMS, for some scenarios.