The changes in question would allow Facebook to tailor ads to you using your social behaviors, and show you ads on external websites. Pretty much, anything you like or link or share would be used to market to you.
The voting starts today, and runs through June 8 at 9AM PDT. You can cast your vote here. The process is working similarly to the way it did in 2009, but in its statement today, Facebook said that it's going to "review this process in the coming months ... to determine whether it appropriately reflects the growth of our community and business and to ensure it still serves its original purpose." Which certainly sounds like it could mean the votes have become too much of a hassle for the now-public company. [Facebook]