The service was down for about 20 minutes, and the outage appeared to have been widespread. No word yet on possible cause. During the blackout visitors saw an error page that said “something went wrong” and the company was “working on getting this fixed as soon as we can.” Facebook had an average of 829M daily users in June, up 19% from last year.

Even though the outage was short, it follows at least two other service problems: Facebook had an hour-long global outage in early August and was down for about 20 minutes on June 19. No, it’s not an earthshaking event — and Twitter is already filled with joking tweets about whether workplace productivity increased, or Facebook users struggled to deal with other people face-to-face. But outages like this have to be worrisome to investors who wonder whether the company’s becoming overvalued with shares trading more than 82 times earnings. Last week Janney Capital Markets’ Tony Wible downgraded Facebook to Neutral, saying that buyers are “continually expecting [Facebook] to beat” earning estimates — and could easily become disillusioned if the company failed to deliver. Shares fell 1.1% today.