I took a look yesterday at Mozilla Prism. So far, i'm not particularly impressed, though I have to do a little more investigation into the webapp.js file and see what XPCOM stuff I can tap with it. As it stands, it seems like it's just a simple way to open up a chromeless browser window from the desktop instead of having to click a bookmark. Largely uninteresting, when compared to things like Google Gears and Adobe AIR.
Tonight i'm going to tap the Google Gears libraries a bit and see if there's anything in there that could be combined with Mozilla Prism to make something really cool.