So, now it finally occurs to me. Google isn't really interested giving people free email. Google wants to be able to definitively answer the eternal question: how many hops does it take to get to Kevin Bacon? By making Gmail invite-only, and being that Google keeps information about who invited whom, and further given that Google has the worlds most powerful search tools, can there be any other conclusion than that Google wants to play a giant game of Six Degrees? If everybody in the world ends up getting a Gmail acccount, then they'll know, won't they? And with information like that at their fingertips, who will be able to stop them?