Tsirist suggested this earlier today, and I think it's a pretty good topic, so let's just do it today.
Currently, on each user's page you can see who they were invited by. However, that's the full extent of what's shown about invites right now. The opposite relation isn't easily public (that is, there's no way to see a list of all users that were invited by someone), and you can't even currently see a list of which users you've invited yourself.
Some people think that these invite relationships should be more public, and some people think it should be even less than it already currently is. For example, some people want to be able to invite others without those people knowing their username, which is currently impossible.
I think that at least tracking the "invite tree" is important overall during the invite-only phase, but it doesn't necessarily need to be public information to serve this purpose. What do you think? Should we show more information about invites? Less? Leave it exactly how it is?