Viewers of our recently concluded Titanfall livestream will have seen these issues first hand. No word yet on when this will resolve. It's just hitting the end of the work day on the East Coast, so the Titanfall servers are about to experience a crushing load.
Update: At 10:47PM ET, Xbox Support reported the problem was resolved. It recommended users perform a full power cycle if they're still having troubles - that's holding the Xbox button down for five seconds to turn the console off, then waiting 30 seconds to turn it on again.
Update: Microsoft statement on 3/12/14: "Microsoft is investigating an issue that may interrupt customer access to some Microsoft online services. This is unrelated to the launch of Titanfall and the Xbox Live service is up and running. The issue on Xbox is resolved, but unfortunately a small percentage of Xbox One owners may still experience a sign-in issue on Xbox Live, which can be fixed with a cold reboot of the Xbox One by powering down, unplugging, waiting 10 seconds, plugging back in and powering back on. The Xbox team sincerely apologizes for the interruption."