When we created the initial fake-brochure site, we thought it'd be a fantastic laugh if the fictional shipbuilders had their own intranet. If you filled in the form on the brochure site (specifying your name, email address and favourite species of frog) we followed the occasional mail about the game. Then, one day, folks got a mail from the intranet admin, "Chris Stevedave", giving folks the link to the intranet and the current password, which was hurriedly followed by a second mail apologising for the accidental mail leakage and urging customers not to click the link, then a third email noting that Chris Stevedave had been demoted to Bilge Emptier Third-Class. It worked fantastically (so fantastically that some people really did send the emails back, reassuring us that they hadn't looked at the site) everyone poured into the Starlight Lines intranet.The Post That Cannot Possibly Go Wrong
Have a wander around the intranet. Look at the wireframes, enjoy the status reports and play with the currency calculator.
Then go look in the forum.
The idea was to present a read-only Senior Management forum in which you'd see some of the key backstory characters getting on each others' nerves. But we figured there should probably be a writeable forum for the lower-level employees, so I spent half a day hacking up a stupidly basic forum system and forgot all about it.
Six months after the site launch, I happened to peek at the employee forum and there were ten thousand posts in there.