I think it depends on how you feel about the social icons. If you need them to have the spotlight and be the first things that you want your visitor to see, they should be at the top.
Generally speaking and from my own observations if you place them at the bottom they become a bit of an afterthought as, I feel, the attention span of the viewer tends to decrease as the page scrolls down further and further.
Though as djsmiley said it might distract your users from your content but to be honest I think it would not be a problem if they are not very intrusive.
I tend to think that visitors don't really mind that much unless they are big and obtrusive, that's why I would opt for a discreet top-of-the-page option.