Like a lot of the users here, I've gone through the steps to become an Ubuntu Member. I won't reiterate the details of what that means but recently it was announced that certificates would be available for Members and I'd like to cash that chip in now.
The problem is the form asks when I became a Member... And I'm not sure. I suspect it somewhere in October 2011 because that's the last time I edited my wiki page.
Is there a public registration of Ubuntu members that includes their registration dates?
If you became an Ubuntu Member through the direct way you can see when, in Launchpad. On memberships page mentions "Member Since"
If you became an Ubuntu Member through the indirect way (ubuntuforums.org), then you can search for your application in UbuntuForums and check the last message. For example my application is here and the last message from Elfy indicates that I became a member in November 17th 2012. Alternatively, a page exist in Launchpad for Ubuntu Forums Members
Launchpad keeps this information. Take a look at
https://launchpad.net/~you/+participation
. Start from "Ubuntu Members". If you are an indirect member (or became a member indirectly), then you may not see a join date, but you will see the groups that cause you to be an indirect member. These should lead "recursively" to a series of join dates, and the earliest one is the date when you became a member.For a hacky way, Googling
site:irclogs.ubuntu.com congratulations oli
shows links me to the#ubuntu-meeting
log where people were congratulating me for becoming a member.