I've being a hard-core Firefox fan but now Google Chrome is tempting me very much!!! First it was the Grease Monkey scripts that Chrome supported and now there are about 100 useful (almost similar to Firefox) extensions in the Google Chrome Extension website!! Installing an extension does not need a restart (well, uninstalling doesn't need either!)
Well Stumble Upon and some neat extensions are rocking Google Chrome!!! True that Chrome does not have a huge addon repository like Firefox but I'm betting on it!
Install the latest Developer Preview of Chrome and try out all those neat extensions!
Google Chrome Extensions