With the addition of Server Fault and the future addition of Super User, I can imagine it gets relatively hard to keep track of all that is going on without having three windows open at the same time and constantly refreshing each of your recent activity pages.
Would it be possible/feasible to create some sort of mini-site that would allow a user to keep track of their account statistics over all the sites and see the recent activity on them (new comments, answers, rep gains/losses, etc.) in one place?
All I am really looking for is almost a clone of the current Recent Activity page (the one you click on the envelope to get to) that would show the activity from all the sites (as long as you have them linked, such as with the same OpenID).
If you wanted to take it another step forward, you could take the personal profile page and modify it to allow for the inclusion of all sites at one time as well.