I received a similar package from my participation in the English Language and Usage site (I was a temporary moderator there while the site was in beta). The letter that came with it had several intentional mistakes noted with copy-editing marks, which I thought was a nice touch.
The T-shirt, however, un-intentionally misspelled the site's name (see http://meta.english.stackexchange.com/q/1926); they sent out another batch of shirts several weeks later, so I now have both a good shirt and a special limited-edition shirt.
The T-shirt, however, un-intentionally misspelled the site's name (see http://meta.english.stackexchange.com/q/1926); they sent out another batch of shirts several weeks later, so I now have both a good shirt and a special limited-edition shirt.