While goining through code,saw this interesting stuff..basically used to specify the typename of a base class and its associated code-behind class. Check this on MSDN .
We can refer the 1.1 framework compiled dlls in Web applications developed in 2.0 without any extra effort. However we can not refer the 2.0 compiled dlls in 1.1 framework application the reason is well illustrated in the thread at ASP.NET Migration forum which says : using COM Interop it won't work because even if it uses COM for "interoperating" it still needs the .NET Framework to run. Since you cannot load 2 versions of the .NET Framework in the same process it will end up running against .NET 1.1 and fail.
However this thread says there is a workaround to refer 2.0 compiled dlls in 1.1 framework application using MSBuild ..!!
With the introduction of Master pages in 2.0, we can now design the page which contains contents repeated on each page -like menus, navigation, logos. We can also combine the functionality used by all web pages at single place and derive all our pages from this master page...
Here is an excellent article on master pages by Scott Allen - providing tips,tricks and traps.
Microsoft also provided 4 design templates based on the category. You can find them here.