It's a ticker of the amount of spam emails that have been killed (before they got to a member's mailbox) since midnight. It's a huge number, and ticks along in real time. The systems by which that data gets from one place to another, and finally gets represented on screen for the user, is equally big. This scale issue has been one of the things that has been hard to get used to over the last year, but I think I'm finally getting it.
One of the cool things is the architecture by which data is cached (or not) depending on the responsibilities of that data and how it will be consumed (all in an effort to conserve network resources). Also, equally cool is the ability to embed web stuff in the proprietary AOL screens and make it look like it's totally normal. That sort of thing makes me hopeful that more "normal" web technologies will be used to present users with the content they are there to consume, and thus make my skills more useful :)