There are sites similar to whoisi popping up all over the Internet. Each one claims to help you keep track of your friends and each one of them have the exact same qualities:
There's a basic problem with those steps. Every one of those sites requires that you have your friends sign up and partake in the site, make the same friends over and over again, and hopefully find the site useful. The result? Social networking overload. Friends uttering "ugh, not another fracking account that I have to take care of." Every site needs to scale and handle millions of users to have the kind of reach that any one individual needs to be able to reach enough of their friends.
Instead of asking you to sign up for an account, you can just start using whoisi. Find someone on the site you want to follow? Just click the "Follow Person" next to their name. No signup, no nothing. All it does is set a cookie. And if you want to save that login so you can connect later or log in from another machine? Check out the "Login Later" link on the right hand side and bookmark the magic url. It's as easy as that. You can stay as anonymous as you want.
The real difference between whoisi and other sites is the way that keep track of your friends. Much like an RSS reader where you add feeds of people you know and keep track of them, whoisi asks you do do the same. Except that you're asked to create entries for your friends first and add all of their feeds. That small amount of work that you've done makes it easier down the road for someone else to come along and follow that person as well. Your friends don't have to participate in whoisi for you to be able to keep track of them, but if they do down the road, you've made it much easier for them.
Whoisi borrows this idea from Wikipedia. That collectively humans can build a great database of knowledge with great collaborative tools. Whoisi doesn't use robots and doesn't use spiders. Instead it relies on humans who are interested in what fellow humans are up to.
Whoisi uses a time-based approach to seeing what your friends are doing. No more read/unread status indicators or mail-like 3-pane views. Just a very simple and elegant flow of information from your friends. You can scan quickly and see what's going on, look at what you want and then move on to the next thing. It's about flow.
If you find objectionable material on the site (adult material, spammers, the main public feeds from places like Twitter or FriendFeed) and if they are not related to a specific person, you should always feel free to remove it. As a public resource, it's up to everyone to keep the site free of things that make it less useful to everyone. Don't be shy about editing.
Whoisi is still an experiment. It might work, it might not. But you should try it out and see if you like it.
For more information about whoisi, please see the original post that announced it. It has a full walk-through and description.