Often, I'm reading a really long answer, and I scroll down to read it. Then, when I want to vote it up or down, the the voting buttons are farther up the page (because I scrolled down), where I can't see them.
Yes, I could scroll all the way up, which I usually do, but some users might be too lazy to do it. Also, since they can't see the vote button, they might forget to vote. And, it's annoying to have to scroll up, so some users might just not bother to vote.
What I propose is that we implement something similar to what OMGUbuntu does with their sharing buttons. Basically, when the voting buttons are not visible because a user scrolled past them, they should have a fixed position on the screen. However, once a user has scrolled past the answer or question in question, the voting button for that specific answer or question can be hidden again.