I've been learning jQuery over on Codecademy and I wanted to make something practical so I made this Greasemonkey script to show the number of unread PMs next to the account alerts.
<img src="https://dl.dropboxusercontent.com/u/8367729/construct/gmscripts/PM_Alerts.PNG" border="0">
Here's the script if you want to try it out:
[In Firefox you need
In Chrome, use the Tampermonkey extension OR save that file to your computer and drag 'n' drop it onto the extensions window.]