Show a user a notification on their blog birthday.
Inspired by @TwBirthday on Twitter, this shows a simple message in the admin panel on their blog birthday.
"Happy 3rd Blogger Birthday! You've been around since 11 August 2008."
"Happy 7th Blog Birthday! The first post on this blog was on 19 November 2004."
"Happy 1st Blog Birthday! This blog was first registered on 23 July 2010."
Caveats: - Old WordPress admin accounts have a registration date of 0000-00-00 and never have a blogger birthday. - Blog registration starts when you turn on WordPress multisite. If you did this, the date may be off. - First post assumes that there a post_id=1 and uses the date off that.