Browsing the site always made me a bit angry (at the politics) and a bit sad (because someone else always seems to be on some impressive vacation). Then I'd close the browser be angry at myself for wasting time I could have invested in learning something or creating something.
My #1 fear was that I'd feel out of the loop, but I honestly don't. I've yet to have anyone mention something with a "didn't you see that on Facebook?" A friend of mine tried the same experiment and says he's also happier. If you catch yourself left with a bit of pensive sadness after using the site, try taking a hiatus and see how it feels.