I have only been in one position where I was able to specialize other than specializing in MS development (Windows, SQL Server, VB, .NET). The one position where I "specialized" was a short-term contract doing report development in Reporting Services, but even there the data source was DB2 on the iSeries so I was also learning IBM's implementation of SQL as I wrote the data access code as well as the display.

In my current position I am responsible for SQL Server Administration, Database Development, .NET development, and some Visual Foxpro. The diversity makes life interesting, but I also cannot become an expert in any one area, and SQL Server and its subsystems are hard enough to try to keep up with.