Update: the extension is now available on extensions.gnome.org.
Gnome 3 and the shell look really great, but there are a few things that annoy me. My main complaint is that I keep missing IM messages because there is no visual clue that you got a message (unless you are staring at the bottom of your screen exactly when you receive something).
This problem will probably be fixed in the next version of Gnome, see bug #641723, but I wanted something now. That’s why I wrote a simple extension that just displays the number of conversations with unread messages. To install it, just clone the git repository and execute “make install”.
The extension is unpolished, it does very little, the code is horrible and I didn’t pay any attention to usability; I just wanted a quick fix while waiting for upstream to fix the bug properly. Nevertheless, I hope this code will be useful for other people too!