IsNullOrWhiteSpace is a new method introduced in string class in .NET 4.0. While this is a very useful method in string based processing, I attempted to implement it in .NET 3.5 using char.IsWhiteSpace() . I have found significant performance penalty using this method which I replaced later on, with my version. The following code takes about 20.6074219 seconds in my machine whereas my implementation of char.IsWhiteSpace takes about 1/4 less time 15.8271485 seconds only. In many scenarios ex. string...(read more)