Some observations on the last n releases:
Throughout the Ubuntu development cycle, there are daily “snapshot” CD images produced. If you’re fortunate to live in a country where most of the “broadband” online population are not capped at 1GB per month (and a presidential hopeful who doesn’t keep singing “bring me my machine gun“) then you can download these during the development cycle to boot (daily-live) or install (perhaps in a virtual machine) to check on the progress or help with testing. These culminate in the actual “gold” release image.
Therefore, if you have one of these images from near the end of the development cycle, such as the release candidate, you can rsync to the latest image available on release day, and that will download the differences between the iso you have, and the final daily image – which will be identical to the release image, even though the daily image will be named something like jaunty-desktop-i386.iso and the corresponding release image named ubuntu-9.04-desktop-i386.iso. Rename it, and you’re done!
(Check the MD5SUMS after the release is announced, to be 100% sure you have it. There is always a small chance of a change to the ISOs on release day if some major “ate all my data” bug is found – so if you do have problems, remember that it comes with no warranty…)
Now, for kicks, go and lurk on IRC in #ubuntu-release-party and watch the masses rocking up to ask “Is it out yet?” Note Alan Pope’s list of Things Not To Say, and don’t go gloating that you have it already – you’ll only be kicked from the channel by the ironically named partybot.
Instead, burn write it to a USB stick (CDs are so early 2008) and get installing!