Fotiman - 7:39 pm on Jul 27, 2011 (gmt 0)
1. To increment the +1 count, the visitor must have a Google account, must be logged in to their Google account and must have a public profile.
Isn't the same true of the Facebook and Tweet buttons as well? That is, in order to Facebook Like something, you must be signed in to Facebook, and in order to Tweet something, you must have a Twitter account. The button doesn't make any sense otherwise, because then you could just +1 your own page a million times.