On certain logins, you get a login gift--either an item that appears in your inventory, which you can keep, or an npc that will follow you around until you log out and then disappear.
On the 42nd login you will for example get the following message:
This is your 42nd login. You suddenly discover a piece of paper in your hand, something froths up in your mind and you just have to write it on the paper. Afterwards you stare blankly down at the paper not remembering what you just wrote.
The paper itself holds a reference to the Hitchhiker's Guide to the Galaxy and reads:
What do you get when you multiply 6 by nine.
|3||Cabbage||Will follow you|
|10||Fruitbat Flavoured badge|
|42||A piece of paper||Contains the Ultimate Question|
|200||A hairy cat||A hairy cat that will spout cat-advice and follow you|