Not very OS X-ish, IMHO. For starters, the expansion arrow has to be double-clicked, something that us mac users always only need a single click. The look also needs some cleaning up (higher-res icons, etc).
Do we really need another entrant into this already crowded space (Fire, Proteus, Adium, not to mention each service's own client ala AIM, iChat, Yahoo, MSN).