I've never been too impressed with it. Fring seemed okay if basic (Installer.app version)... assuming they upgraded its feature set, it could be good. Is fring definitely not going to be developed as an app store app? I have not seen any commentary on it one way or another (the fring blog is oddly completely silent about the 3G iPhone).
I was kind of hoping someone would bring libpurple to the iPhone (what backs up Adium and Pidgin).