There are many possible reasons for the sort of issues you're describing (low spec machine, too little RAM, bad page file configuration, a need for a cache clear etc), but there's a reasonably easy way to avoid it that may work for you. It works for me very well indeed.
I browse using Opera, which gives me an easy way to switch browser plugins on or off (via the F12 key), but I'm sure there must be easy ways to do the same thing in IE or Firefox or whichever browser you use.
With browser plugins off, all I see on those YouTube posts is a link. Nothing loads, nothing connects to anything else and everything stays nice and quick.
If I want to see one of these videos, I click on the link and it takes me to the page at YouTube (or whichever video site the link is to). Because browser plugins are still off the video still doesn't show. However I open a window to http://keepvid.com/
and copy the web address from YouTube (or whichever) to KeepVid. Now I can download the video to my computer and watch it whenever I like.
This may well be a far more drastic solution to your problems, but at least it's now an option for you.