I'm browsing using Firefox 30.0 and the front page is lagging when scrolling. Using my scroll wheel lags and my fan even spins up when I grab the scroll bar.
I've also noticed the issue and can't figure it out for the life of me. Thanks for pointing that out, though! If anyone has any suggestions, feel free to comment. We have stickers! #bribery
It looks like the transforms might be part of the problem. You have an image transform on hover that moves the image up. If your mouse is in the middle of the page and you scroll down, it triggers and seems laggy.
No issues in Chrome, however.