If there's one thing that Google-owned services are known for, it's their uptime, but YouTube's not having the greatest day on that front. The video service is down, and it's down hard: visiting the website returns a 500 Internal Server Error, and neither the mobile site nor the iOS or Android apps are operational at this time. Fortunately, embeds appear to still be working for some users, so you're not completely out of luck. Reports of the outage started to hit Twitter just over 20 minutes ago, so there's no doubt YouTube engineers are on the case at this point. We'll keep you updated on when your regularly-scheduled video viewing can resume.
Update: Breathe easy, friends. YouTube appears to be back up and operational.