I'm using C# and .Net 4.0 at the moment. I'm using SQL Server 2008 Express for the fairly light database load I have (it's an installable product not a public web app). I'm using Linq to interact with it. It's been a great experience for me so far. The Linq integration with SQL Server has saved me a ton of time. I've had to write a few stored procedures so far and that's it.
I know C# better than any other language so it was an obvious choice for me. The option of at least offering a Linux product on Mono has crossed my mind a few times so that's a plus too.
One of my pet peeves (and it is Microsoft's fault for such a terrible naming scheme) is how people use LINQ interchangeably with LINQ to SQL. LINQ is a language feature used by other frameworks (LINQ to XML, LINQ to Objects, etc). LINQ to SQL is an ORM.
I know C# better than any other language so it was an obvious choice for me. The option of at least offering a Linux product on Mono has crossed my mind a few times so that's a plus too.