I was happily using my Sun Ray session one day and then it stopped accepting keyboard input. Nothing I tried could make anything other than the BEL sound happen. After posting to an internal list at Oracle carried over from the Sun days, the ever helpful and venerable Alan Coopersmith clued me in. I must have held the shift key down for five seconds, turning on the "only accept long keypresses" feature. This is great for people with Parkinson's but thankfully I'm not there yet. But it's nice to know GNOME has my back.
If you run into this problem you can disable it by going to System::Preferences::Keyboard, in the Accessibility tab, and ensuring the "Slow Keys" checkbox is not checked.
You may also want to uncheck "Accessibility features can be toggled with keyboard shortcuts.