SQL Server seems to have really terrific tools and features, enough to make me consider using it instead of MySQL, even though I'm doing development on an open source stack.
Has anyone developed an app on a non-.NET stack and chosen to use SQL Server as your backend?
What were your reasons for doing so?
I have not done development with an open source stack and Microsoft SQL Server, but I would just like to say that SQL Server 2008 is terrific, and the developer experience is much better than with any other database that I've used. However, if the open source stack appeals to your philosophical side very much, you won't have any problems with MySQL I'm sure.
In other words, the way I see it is if you don't really care about keeping it open source all the way, then SQL Server is the way to go, but if you do, just use MySQL, it'll get the job done.
Don't ignore postgresql -- every bit as open as MySQL, not in the middle of a muddle (caused in MySQL's case by acquisition by Sun then by Oracle, core developers leaving, forks into Drizzle, MariaDB, OurDelta, ...), AND just about as functionally rich and SQL standards compliant as MS SQL Server if not more (I miss recursive CTEs a lot when I have to use MySQL -- both SQL Server and PostgreSQL have them, though, just as the SQL standards require!).
At the recently concluded OSCON (the Open Source CONvention) 2009 in S.Jose, my totally subjective impression was that the MySql-and-forks folks were mostly busy needling each other, the many Microsoft folks were totally mum about databases, and the PostgreSQL folks were the ones discussing, teaching, explaining issues such as scaling, database design, optimizations, deployment options, and so forth. I've long loved PostgreSQL, but with the current 8.4 release it really seems to have reached a peak!
I would just warn you to be careful committing to SQL Server on a non-.NET platform before you have seen performance metrics. I once had to pair Java with SQL Server 2008 and found the performance unacceptable. The Microsoft provided JDBC driver was pretty 'subpar' ( transactions were extremely slow). A friend recommended the jDTS open source driver, which would not work with the database unless the database was set to use the SQL Server 2005 engine. Performance was a little better then, but not what I had expected. I then tried installing SQL Server 2005, pairing it with the same jDTS driver, and finally succeeded in getting the speed I desired. But, as a database platform, it is a really nice system.
There are neither advantages or disadvantages.
The code and schema will probably have more effect than the choice of language used.
That said, MS spends a lot time tweaking the .net SQL stuff.
Where I have worked with the MS jdbc driver (as dev DBA), it's pretty rubbish: no support for domain account or SQL Server SSL encryption. The Java guys I work all use jtds now. Although, we're on a corporate Solaris platform.