Although Chrome/YouTube power users might already know an even easier shortcut (skip to the part in the video you want to share, right click, and select "Copy video URL at current time"), using YouTube Time is almost equally as easy to use (perhaps easier, if you're not so good at remembering shortcuts).
Copy and paste the URL, input the exact time you want the URL shortcut to designate as your starting point, share to your heart's content! The site spits out a link with the time designation included. I made a shortcut link for Maxwell's presentation about "techorating" (full version below).
Via Swiss Miss