I'm glad that people are on board with the idea! (and it certainly doesn't hurt to have yegg's approval) I was trying my hand at a text adventure prototype too: did it in Python but it just parses input and cleans it up right now.

Maybe something less prominent? I don't think the achievements should overwhelm the rest of the page.

Moderator

Achievements might be heavily distracting to users, unless they are done correctly. For instance that mockup should be much more centered, and should probably just be a small popup window in the corner, like most achievements systems.
At this point a giant YOU HAVE DONE AN ACHIEVEMENT box would only server to annoy the user.
I think a simple accounts system would be necessary to keep track of achievements (perhaps a simple username, password, and email, which could be used to share duckduckgo settings over multiple computers?), preferably one that doesn't require a whole lot of personal information, and one that doesn't demand you sign up if you don't want to.

The text adventure seems like a more fun idea though.
Perhaps an achievement could be made if the user wins.
Also, if a achievement system was added, perhaps zero click info should be able to integrate with it to an extent.
e.g

FLIP OF A COIN: use duckduckgo to preform a coin toss.