Are there any other Gecko based apps you use? I can't think of anything besides Songbird right now.
Have you head of the Prism plug-in? I am totally hooked, all my online apps I use (Gmail,Google Calendar,Nagios,etc.) have as Prism apps. It is essentially the Firefox browser with all the browsing interface items removed. Basically turns a webpage into desktop app. They still need to figure out how to force a reload or dump the cache, but other than that its nice to run with my web apps in separate processes than my browsing.