This is something I've been exploring and I'd love to hear more about how you'd like to use chat with SBS. For example, when or about what would people want to chat? With whom? Do they already have an IM client on their desktops?
While we have IM (used by some), Webex (can use the camera), and live streaming for corproate events, we wanted to have a way for an executive to broadcast a live video feed, have a real time chat, and have it all on one page. It is a bit of a stretch for any one program. The discussions are a sort of asyncronous chat. Having a widget to just show one discussion could simulate a chat function. Having a way to pipe in the video feed would is a bit more of a challenge.
Bottom line is that the executive asking for it does not want to piece together the bits and pieces we have available.
Ford Motors has used an embeddable flash app from CoverItLive -- http://www.coveritlive.com/ and we're looking into it too.
Basically a moderated chat / liveblog / eventblogging system. Go read about it.
Intel is currently using the ParaChat enterprise chat client widget on our pages, but would love to see this functionality built into SBS. We are going to be hosting our next chat on Dec 8th, 2009, feel free to come check it out. The chat will be hosted in our Server Room community.