What are the reasons to use SQL Server instead of MySQL with a complex .Net project?

My pro/con list for MySQL vs. SQL Server for .NET projects would be:

Pros to MySQL:

1. Cost

Pros to SQL Server:

1. Better tooling support, especially for .NET (Entity Framework + other ORM support is MUCH better)
2. Better Visual Studio support
3. Better integration support, especially if you want to do things like Silverlight + RIA, etc.

Have a look at

• DBMS Comparisons: MySQL 5.0 vs. Microsoft SQL Server 2005
• Comparison of Microsoft SQL Server 2005, MySQL 5, and PostgreSQL 8.3
• Microsoft SQL Server vs. MySQL
• MySQL or SQL Server: Look beyond politics and hype when deciding which to use

With SQL Server, you can have better tooling integration ( such as designers) between your entity class and your database schema.

You can just drag a database and drop it in the designer, and viola! All the entities mapping to the tables and their relationships are generated.
_{(source: scottgu.com)}

As for MySQL, obviously licensing cost is an advantage