Greasemonkey script lets YouTube videos buffer
I'd rather just cache the whole clip first then watch it - which is precisely what Youtube Buffer Video for Greasemonkey is designed to do.
Install and activate it, and autoplay is automatically disabled on YouTube pages. Sit back and let them buffer as long as you like, and click play when you're ready. My ISP isn't always running at peak performance, so it's nice to have control over when playback begins.
There's nothing more to it. Like many Userscripts, it's a small, simple tweak that might fix a web site annoyance you figured you'd just have to deal with.