I think that this is new in Sametime 8 – I certainly never noticed it before in previous versions
If you choose View > Maximise and have two monitors the shared screen appears on your second monitor leaving the Sametime interface still open in the Primary monitor. This lets you see chat and access the controls
I have often found Sametime disappointing and until I moved to Vista we tended to use MS Netmeeting over VPN between our offices to screen share peer to peer. With it not being possible to Netmeet between XP and Vista machines ( MS what were you thinking ? ) we upgraded our Sametime server and have been pleasantly surprised
As an aside you would think that the Lotus spell checker would recognise Sametime wouldn’t you !