I LOVE Iris browser... I'm honestly surprised this is one of the few threads about it (there were a few back when it was referred to as Torch Browser, before the current version).
Yes, I use it primarily for Facebook as well. A little trick that might be useful since the iPhone has slightly different screen dimensions: set the zoom view to match page width. Then the page formatting fits better.
It never occured to me to change the icon to Facebook- that's actually not a bad idea. You can totally change icons by finding an appropriate icon contained in a .dll, and referencing it by the link (lnk) in your programs dir.
More on this:
http://mobile-sg.com/simpleblog/arch...ost.asp?id=849
As far as icons go, yes you can absolutely change the icon: