This question reminded me of a big complaint I had and forgot to voice before.
I happened to be busy when the SO Beta was happening and was unable to participate. When you posted that blog entry with the proposed tags for the site, there was a "Founder" badge and a "Beta" badge proposed. People quickly said that all badges should be attainable at any point. That is to say, if someone joins StackOverflow today, they should technically be able to get every single badge on the site. Badges are akin to collectibles, and if someone says there's this one collectible you can never have it kind of takes the fun away from it.
You removed the Founder badge, why not Beta too? You could still mark it in their profile somewhere they participated in the Beta, I want people to get their recognition for helping the site out, but I don't think it's really fair to other users to have a badge you simply cannot get.