One of my brothers-in-law (yes, that is the correct pluralization of this hyphenated word!) blogs only when he is glum, dreary, blue, down in the dumps, in the doldrums,....
His blog (or mySpace or whatever) consequently reads like someone's suicide note. If you didn't know him, you'd worry.
However, I'm finding that I don't want to blog when I'm in that state of affairs. 1) I don't want to broadcast my state of mind to all the Internets everywhere. 2) Broadcasting it to all the Internets everywhere is creepy at best and dangerous at worst. 3) Re-reading it later sounds like whiny complaining. (Did you ever reread any of your journals? I re-read a Middle School Journal...whoo nelly was that ever soaking in patheticness! Ick! As cj's daughter says, "No thank you!")
I am doing a considerable amount of journaling in my private journals, though. At least it gets it out of my system, even if it's maudlin and filled with histrionics when I read it a decade later.