title: What .NET version to choose?
body: <p>I am writing public .NET class library version for our online REST service and I can't decide which version of .NET to choose.</p>
  
  <p>I would like to use .NET 4.0 version but such compiled class library can't be used in .NET 2.0 version? </p>
  
  <p>Maybe there is statistic how many developers use .Net 2.0 version?</p>