This O2 site was slightly different from the rest, as this site was directed at specific O2 members only.
Basically O2 wanted to improve their messaging service, so thought the best way to learn the bad points of their service is through its customers, that's where the O2 Guru websites comes into it.
O2 sent emails to 100 of its customers that use messaging most, this email contained a unique URL (supplied to O2 by me) for that user where they could register with the site. Once registered, they would be set many tasks and report back their results to help improve the O2 messaging service.
There was no crazy functionality on here, but virtually all of the site is content managed. There are three types of user that can register for this site, and each type gets their own content on every page. So if you are a part of group one you will see a certain piece of content on a page that group two for example wouldn't be able to see.
The same goes for the Polls, Tasks, and Discussion Forum etc. If you are a member of one group you won't see what's going on in the other group. Quite a simple piece of functionality from my point of view, but very effective nonetheless.