At the request of my brother, looked at Pidgin's mail notification dialog this evening. The Ubuntu package takes ages to build, unfortunately. The reported bug was that the 'Open Mail' button didn't work - looking at it, it's possible to select the mail you want to open on some services now, but by default nothing is selected. There's some code to desensitize the button in that case, but the initial state isn't set. My preferred patch would be to use GTK_SELECTION_BROWSE and some code to ensure that an email is always selected... I hacked together something that works for MSN, at least. It's short enough that it might not have too many serious bugs.
I'm still not a big fan of Pidgin's UI design choices, I suppose. Perhaps one day IM will be built into the desktop and I won't have to worry.