Voting is pretty easy, actually - click on the words "EditText" at the bottom of the TipsForBeginners page, and bump the number of votes for your choice by one. -- BillTrost
An alternative approach, which does not involve the voter in arithmetic of any kind, is described in TwoTouchVoting.
Q: How do you know who are making the changes?
A: You could try to figure it out with the RecentChanges page or RecentPosts. -- PieterVerbaarschott
See WikiBallotBox for even more info.
See http://www.hanoi.dynu.com/~hanh/phpwiki-1.3.3/ [BrokenLink] for survey embedded in wiki page.