It was always comfortable to use features that are provided and supported by Microsoft (when it comes to Visual Studio and the like) so that we won’t be in trouble in the future, at least for me.
For this reason, I always think twice (or more) before touching anything that is open source, to be used with production code. The ASP.NET AJAX framework was so easy to use because of the pre-built controls provided by the Ajax Control Toolkit team. I had very few occasions where I needed to write some JavaScript code in the applications.