Tuomas has some really nice mockups of a little notification baloon on his website. Today, he is suggesting that rich content via HTML is the way to go. I agree. Those things look awesome.

Using HTML for the content would lower the bar and allow for a great uptake among both developers and the general Web-saavy population. Plus, wouldn’t it be great to whip up something that nice looking on your desktop in a script or such in the matter of a couple minutes (or less)?