I played around with Prism a few months ago and was fairly impressed. Prism lets users split web applications
out of their browser and run them directly on their desktop, Also known as a Site-specific browser. Prism has recently hit 1.0 beta, and is available for OS X and Windows. So far I’ve only used it for Gmail and Slacker radio and I recommend doing a quick search on flickr for “Gmail icon” or “Slacker icon” (or whatever site your making the SSB for) then use that image. If you don’t specify a image it uses the faveicon by default which is only 16 pixels square.
Another great SSB that I have been using on my Mac’s for a while is Fluid, Although as of this writing fluid has only reached version 0.9.6 so if your wanting something a bit more up to date you may want to stick with Prism.