Why should it be slow ?
Indeed, C# is compiled to 'Intermediate Language', which is JIT'ed at runtime, but this can give you a performance advantage, since the runtime can generate the most optimized for the platform the code is running on ...
Depending on the application that you want to write, the 'speed' of the language will have a minor impact.
The performance of your application will mostly be determined by the way you design your application, if you make good uses of the tools / technologies you use , etc ...
Sure, C# is not a silver bullet, and there are projects where you shouldn't use it, simply because it is not the right tool for the job, but it will do just fine for most of the business / enterprise app's.
