Looks like Google Chat has implemented sound notifications. DownloadSquad reports that "Oddly, you need to have Flash enabled in order to hear the ping". Not exactly odd to me, as I mentioned before, there's no nice cross-browser way to do sound in the browser currently without using Flash. Kudos to Macromedia/Adobe for being so widely deployed and useful in this context. If nimble browser development camps like Mozilla could follow Opera's lead on implementing HTML5's Audio interface this would be a Good Thing.