The developer dashboard was a great new feature when SP2010 was released, and now with SP2013 it has been further improved, with the key changes being:

• The Dashboard now appears in a separate window – it isn’t rendered out at the bottom of the page you are diagnosing any more.
• Cumulative page requests are shown, instead of just the last request.  This certainly helps in SP2013 given the use of Minimal Download Strategy (MDS).
• The execution Plan of SharePoint stored procedures can now be viewed.
• The dashbaord is implemented as separate WCF service named diagnosticsdata.svc
• ULS Logs can be viewed through the browser (rather than opening the logs in ULSViewer or Wordpad) – but this should still be done from the server for security reasons
• The Dashboard can now be extended with Javascript 🙂