A lot of us downloaded Day One recently as it went free as part of the 5 Years of App Store promotion. I didn’t think I would write anything1. But after trying it for a few days, I’m really liking it.
Slogger indexes various public social services and creates Day One (http://dayoneapp.com/) journal entries or plain text Markdown files for them. It allows you to keep a personal journal that collects your online social life automatically, all in one place.