I think I first heard it in the movie 28 Days with Sandra Bullock, but I believe it was already a popular saying in AA and other types of self help and therapy.
Personally I publish both the good and bad sides to things going on around me, mainly because I don't believe in whitewashing how things are, and also because I use it to keep in contact with family and friends that are of a distance away.
What I've found is that if there's a stretch where there's a lot of bad news, people will just tune you out, where comments dwindle and activity lessens even when that trend has reversed itself. In my incredibly small and unscientific sample size, it seemed that with negative news, there was a greater chance for people to "tune out", while people I knew that did the "everything is awesome" timelines would have higher then average interaction.
Thought it was interesting at least. I wonder if would be reproducible, or if it's just a weird quirk for the people that I know on there.
I make it a point to blog about my suckage every day, so that if I ever get successful, there's a nice big chunk of evidence of how a person can suck before getting good at something.