Ubuntu 10.04 increase in bandwidth use for daily apt update

I was looking at my linode's graphs today and noticed that my bandwidth use is way up on a daily basis around the time the daily cron job kicks off and updates my apt package lists. It seems to have started about two weeks ago. I haven't installed anything other than the normal security updates, so I was wondering if anyone else had observed a similar behavior or had any idea why the update is using so much more bandwidth now.

~~http://flateric.us/bandwidth.png" />

Thanks for any information you can provide. (Yes, it generally is a low bandwidth server, which helps this stand out.)~~