Its a great concept! A site where people can share invites for different web services which are invite-based only. Instead of searching for invites on the web or waiting for an invite you requested from that particular site, you can go to InviteShare.com and request an invite, and usually you will soon be invited by one of the users.
But the downside is that there is no provision to protect the privacy of users. Once you request an invite, your email address will be visible to anyone who holds an account at the site. Now imagine what happens if a spammer gets hands on your email address. In fact, people have reported an increase in spam in their inboxes after they signed up at InviteShare. Well, every good thing has its price. So are you going to request an invite again at InviteShare?