The team down the road from me at Carsonified have been doing it, and you can do it too.
Fluid is a fantastic free app that turns any web site into a self-contained application on your Mac. If you want to keep your webmail outside your normal web browser, Fluid is what you need.
Thing is, all the apps it creates need icons, just as any app in your Applications folder does. By default, Fluid grabs the .ico files it finds on web sites and uses them as icons, but they don't scale well. Where can you find decent alternatives?
The answer is the Fluid icons pool on Flickr, where a busy community of Fluid users have been busy making a selection of beautiful icons that work perfectly with any Fluid SSBs (Site-Specific Browsers) you've created. The icons in the pool might look weird to start with, but that's because the PNG originals have been converted to JPG format by Flickr's brain. To make use of an icon you like, make sure you view and download the full-size original, which will be the PNG file you need.