is C# worth learning ?
C# (pronounced C sharp) totally worth learning. Its syntax is good and it can be used to do desktop applications, web applications, DLLs, Silverlight (http://www.microsoft.com/silverlight) and mobile applications (for Windows Mobile devices).
The only disadvanted of C# requires the .Net framework to be installed on the computer to be executed, like java needs a virtual machine to be executed. The .Net framework is a lot of rich functions already built and ready for you to use. There are many .Net communities and you can find so many DLL/libraries to attach to your websites and applications to do tasks of all kind, that would be very difficult to do manually (such as full control with Microsoft Office format, without having it installed).
ASP.Net is a powerfull language for web applications. C# can be used as server side script with ASP.Net.
C#'s performance depends on how you develop your application. It can be quite fast (still can't replace C++ and Delphi).
All in all, C# is a very useful language and easy to use and learn.