I really like BrowserHawk. During the heady days of the browser wars, and even now in the calmer waters of almost compatibility there it's sometimes really reassuring to know that there are some simple, reliable ways to know what the users browser is and what plug-ins it's got without having to write hundreds of lines of JavaScript with lots of try statements or go through complicated multi page refreshing detection routines to see what version of Flash or Quicktime you can target safely (or allow you to elegantly guide the user through getting exactly what your page needs to run)

Until now Silverlight was in the same boat. You needed to probe the results of the javascript loader to see if it had found the plug in, or if it was displaying the "click here to install Silverlight" graphic (which pretty as it is, sometimes isn't the best way to go)

I was pleased to discover reading the release notes for the new BrowserHawk detector that it supports detection of the Silverlight Plugin and returns the installed version number so you can make appropriate decisions while rendering the page.

One additional function that, while not Silverlight related, I wish I'd had back in the Big Brother days is the ability to detect and report back on JavaScript errors - until now it's always been difficult once you've released JavaScript laden pages into the wild to track what problems are occurring (and know exactly what the browser configuration is) in order to improve code quality. I hope my successors back in Australia take it on board...