I've been doing a lot of GWT work, and I find the Development Mode to be particularly productive. Unfortunately I frequently seem to lose the "?gwt.codesvr=127.0.0.1:9997" URL suffix that makes dev mode work.
My buddy Jeremy came up with a simple fix: a bookmarklet that adds the URL suffix to the current URL. Drag this bookmarklet to your GWT-devmode-enabled browser's toolbar:
[devmode](javascript:window.location=window.location+'?gwt.codesvr=127.0.0.1:9997';)
Next time your devmode isn't working, just click the bookmarklet!