The abundant artist blog about Tumblr is interesting. Says it skews young and poor. Under 30 and under $50K income. Realm of teens and college kids. Probably because its so cell phone oriented. Picture people flipping through on cell phones on the way to work.
If you have limited time, pinterest seems to be more worthwhile as its a wealthier and older demographic - people decorating their homes, planning weddings, daydreaming about their perfect kitchen etc.