Yeah I was just about to say this -- I used Sametime via Pidgin (I think it may still have been called Gaim back then) on my work Linux machine and it was actually quite nice.

My favourite Sametime feature within Pidgin was, well, tabs (I can't remember if the Windows client had tabs as well..?), which was revolutionary for an IM client in 2005.

But my secret actual favourite feature was the setting which automatically opened an IM window /tab when the other person merely clicked on your name on their side (because the Sametime protocol immediately establishes a socket connection), so you could freak them out by saying hello even before they'd sent their initial message.