A good point, but it doesn't really invalidate the idea of whitelisting personal e-mail addresses. As someone mentioned above, spam is an economic problem. If the only e-mail addresses that weren't using whitelisting were business e-mail addresses (a small fraction of the total e-mail addresses out there) then it would no longer be profitable to send spam.

I saw a wearable once that stored energy from the compression energy in your shoe when you walk. If you batteries get low.. go for a 15 minute stroll...

cool, eh?