Worldcon site selection ballots can be taken in person or carried by another to file at Anticipation, or mailed. Mail-in ballots must be received by the July 15 deadline.
Voters must be members of Anticipation, and buy a voting membership in the 2011 Worldcon (which automatically becomes a Supporting Membership in the con.)
Reno is the only bid to have formally filed, and the bidders, urging a higher turnout, are reminding fans of a potential savings if they vote in site selection:
Additionally, if you vote, you can convert your Supporting Membership to an Attending Membership for no more than $90, for at least three months after Anticipation.