Anyone with an email account can open a separate account at facebook (for every single email account), just think how many accounts an user can establish (at yahoo,hotmail or google for instance) and do the math with the grossly inflated number of 500.000.000 "unique" facebook users. I, for instance, have more than one.
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Police fire tear gas, detain 200, in Istanbul May Day scuffles (Reuters)
from the article: Anti-Semitic Facebook page gains over 10,000 fans