So we've been doing a bit of work on Empathy lately (but too late for GNOME 2.30 I'm afraid), and trying out some crazy new ideas.
One of these Favourite Contacts. You can now mark contacts in your contact list as favourites, and they will always been shown at the top of your roster (as well as in any groups they're a part of).
Another is Frequent Contacts. This information is generated by the new telepathy-logger service, and shows which of your contacts (on your contact list) message you most frequently.
The telepathy-logger is a new desktop wide logging service in development that applications (such as Zeitgeist) will be able to query to retrieve conversations that take place via Telepathy. As well as recording the actual messages you send and receive it also generates statistics, such as your most frequent contacts. This means information such as your favourite and recent contacts are also available to other Telepathy clients (perhaps they could appear integrated into GNOME Shell along with current conversations).
We're also considering adding Recent Contacts, so you can quickly return to a conversation you have been recently having after you close the window.