The 82nd Academt Awards will take place on March 7th this year.
"Question: Who is Eligible to Vote for the Academy Awards?
Answer: Voters must be members of the Academy of Motion Picture Arts and Sciences. Initial voting is restricted to members of the Academy branch concerned. For instance, when the first wave of ballots is mailed to all members of the Academy, only directors may nominate other directors. Once the first round of voting is done and the field has been narrowed to no more than five nominees in each category, except the Best Picture category, then all members of the Academy of Motion Picture Arts and Sciences are allowed to vote for a winner in most categories, including Best Picture.
In 2009 the Best Picture category was raised from five final nominees to 10. All voting members of the Academy can vote for Best Picture in the preliminary and final rounds, and the preferential voting system will be used to make sure the voting members intentions are accurately represented."
http://movies.about.com/od/awards/f/oscars122504.htm
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That said let me just add that I think it would be pretty cool if we could have a vote to decide who WE THINK should win best picture. Don't worry about not having seen all of the films listed...I am sure that the people voting for the real thing didn't either.