1. Upside-Down Facebook
What It Does: The engineers had fun with Facebook's language settings. This pic shows what happens when you set your language to "English (upside down)," but you can also try out "English (Pirate)" which (among other things) will arrange your timeline by "shots o' rum" and "turns o' yer hourglass."
Current Status: In full effect.
2. The Name Generator
What It Does: This one started with users noticing that if they typed @[4:0] into a comment or wall post, it would change it to "Mark Zuckerberg." As it turns out, that's Facebook's way of calling usernames, and it works for any number. (Zuckerberg came on as user #4, after three test profiles.)
If you want to find the number that calls out your own name, just go to your profile page and, in the url, replace "www" with "graph." You should end up with something that looks like this, with the number on the second line.
Current Status: Still going.
3. The Little Celtics Fan
What It Does: A couple people were poking around on Facebook's photo server when they noticed that if you went to the URL for the main photo folder (maybe hoping to see photos you didn't otherwise have access to), you'd get a picture of this infantilized Celtics fan as the index file. No one was ever able to figure out why.
Current Status: Sadly, they've changed their file system since then.
4. The Severed Head of Christopher Putnam
What It Does: If you type ":putnam:" into Facebook chat or comments, you'll summon forth a thumbnail head of Facebook engineer Chris Putnam.
Current Status: Going strong.
5. The Chat Thumbnail
What It Does: If you put a username between double brackets in Facebook chat (like so: [[russell.brandom]]), it will magically transform into that person's thumbnail pic. It hasn't evolved into an emoji-substitute quite yet, but we've got high hopes.
Current Status: Alive and well.
6. The Quotes
What It Does: On the first few redesigns, if you scrolled to the bottom of nearly any page, you'd find either a cryptic reference to quails or a line from Top Gun in fine print — just what you'd expect from a nerdy 20-year-old.
Current Status: These were part of what defined Facebook as a college thing — so not surprisingly, they didn't live to see 2009.
What It Does: This one goes back to the most famous easter egg of all, the Konami Code. On early incarnations of Facebook, those fateful ten keystrokes would call up a lens flare effect that moved around as you scrolled.
Current Status: Sadly, this one went out with the tabbed browser page in 2009.
Any we missed? Post them in the comments.