Matt turned me on to a new app for OS X (Leopard only) called Fluid. Essentially, fluid lets you create website-specific applications - really just little webkit browsers as their own applications with their own icons. It's really simple to use and (so far) has worked phenomenally well.
I have two web apps that have become an absolute core staple of my daily routine: Remember the Milk (for TODO management) and Google Reader (for RSS feeds). Both of these are pretty "heavy" web apps (containing lots of JS/AJAX/etc) and I had been running Firefox extensions for both which ultimately weighed down my main browser (which is where I do primary development, etc). Having them as separate applications lets me keep Firefox running (a little) leaner, and I also get pretty icons and the ability to "cmd-tab" between them.
The coolest part, however, is that Fluid has implemented icon updating on a few sites (google reader being one of them) to show the number of unread items. Check it:
Now, if I can just get Google Gears for Webkit working (for offline support for google reader & RTM) I'll be one happy camper.
The desktop / web app convergence continues...