I got hit by this bug:
The Aperture 2.1 48MB updater doesn't recognize that Aperture 2.01 is installed. I tried various hacks that have worked for others: removing pref files, removing receipts from all prior Aperture installs, removing the Aperture ID file from Pro Apps, deleting Aperture, emptying trash, reinstalling from DVD using an Admin account, etc.
Not coincidentally, when I run Software Update I'm not notified of the 2.1 update. On my G5 iMac running 10.4.11 and all security updates there's something broken in the Aperture registration department.
I was able to install the 184MB Aperture 2.1 trial version. It recognized my registration key and it includes the "dodge and burn plugin"
Even after successfully installing 2.1 trial however, the updater still does not work.
BTW, the sample projects that are installed from the DVD occupy 3GB of disk space. They're stored in Library\Application Support\Aperture.