At this point I think building on the Facebook application environment on Facebook is too volatile, at least formy current uses and prefer the relative stability of tabs.
Life here at Forbes is a case in point: The company uses Windows computers, bought in volume...well, except formy magazine, where everybody uses Macs...well, except for me, because I'm writing this on a Windows laptop.
It's great because it has an HTTP and FTP server and uses regular HTML to issue the commands making it the perfect match formy PSP, which does not support any fancy Javascripts or DHTML. The PSP talks to the WACI NX via wifi through the network.