I was recently working with Google Analytics and discovered the Google Analytics Tracking Code Debugger. In the past, one of the biggest frustrations I had was that I would make a change and then have to wait until the next day to see if the changes worked. I guess that the time to see results with Google Analytics has been lessened recently but, in my experience, it still isn’t instantaneous. Google Analytics Debugger gives you instant feedback during development:
This allows you to see the results in a tool like Firefox’s Firebug while testing on a local development server. It is much nicer than running tests and coming back hours later only to find that there was an error in your code. I am not sure when this tool was made available, but I wish I knew about it earlier.