I've had the same experience as PhotoGirl. I called support and have a case #: 417992805.
I started with the initial release of Aperture 2.x, and have updated/upgraded regularly ever since. Every update and every upgrade. Internal drive failed. (Covered by an Apple recall.) I had backed up the library and vault — redundantly. I had a valid 3.x serial # (which I didn't expect to need). I figured I had covered all bases.
Having restored everything, I tried to open Aperture. Nope. After having used the application without hassle for a very long time, I was surprised when asked for a serial number. I was even more surprised at being told I had an upgrade serial # and would have to enter my 2.x number. Say what?!
I always register software, and I know I registered both 2.x and 3.x with Apple. Think about what that means. Apple pushes me to register every purchase, and I do. But why do they push? Presumably because they're going to keep my info in a database.
Fair enough. So I register; later they can't find the serial # I registered; but they insist I find it. Mind you, all my registrations are in the same name, same Apple ID, same email, same street address. Apple can't keep my registration info, but they insist I keep it — from over three years past. That or the paperwork Mr. Caggiano points us to (i.e., the advice anyone seeking Apple support would find within the first few minutes). The kind of paperwork few people would keep or, if they kept it, be able to find.
∞ ∞ ∞ ∞ ∞
The telephone support folks were very good. For the best documentation I could find, I sent them an email containing the following: (a) scan of the original installation disks for Aperture 2 and 3; scan of the original intro booklets for both; upgrade serial # for 3.x. I probably sent that info to the wrong email address (firstname.lastname@example.org). Even if the address had been correct, however, I doubt that documentation would have made a difference.
My solution? I gave up on Apple. I went on line and found an original, legitimate, never registered Aperture 2.x program. I bought that program, used its legal 2.x serial #, and got my legal copy of Aperture 3.x running. Yeah. In order to activate Aperture 3.x I had to purchase two separate versions of Aperture 2.x.
Apple must protect its intellectual property rights, obviously. But it should do so in a way that doesn't abuse loyal and legitimate individual customers.
∞ ∞ ∞ ∞ ∞
P.S Irrelevant here, but as a side note: I'm not a habitual Apple basher. My first computer was an Apple 2, purchased in 1977. 48K memory, ordinary 3.25" cassette tapes for storage. My first dot matrix printer cost @$1000.00 in late '70s. Major sacrifice for a newby assistant professor at a small college, with no certainty of tenure.