Sites go down all the time and frankly my blog hosts have failed more often than Disqus.
Nevertheless, it's uniquely frustrating when comments are off but the blog is live - especially if you've just got a good scoop.
Right now Disqus looks to be down. Poot.
Update: It's a semi-planned outage. Disqus, good as ever, got back to me on Twitter in less than a minute!
Update 2: Disqus was down for around 120 seconds. Er, unless it goes down again after this update.