I read a great article about performance and scalability. Some of the issues there were helped me a lot and the rest were sharpen my knowledge.
So, if you are an ASP.NET developer (beginner or senior), It is recommended for you to read that one by Omar Al Zabir at the codeproject site here.
Some if the things that he talks about are: ASP.NET pipeline optimization, Things you must do for ASP.NET before going live, Caching AJAX calls on browse and more...
Worth a reading...