I recently upgraded to 13.04 and have noticed that my keyboard randomly drops keystrokes. Furthermore, it will occasionally cause the last pressed key to "stick", leaving me with "typng that looks lik thisssssssssssssssssssssss".
I do not believe that this is a hardware problem, as the keyboard worked just fine under 12.10 a few days ago. In addition, there are no Universal Settings turned on that would be causing this problem.
I came across this unanswered Ask Ubuntu post that seems to identify part of my problem: Missing keystrokes in ubuntu 13.04
I was able to work around the repeated keystrokes problem by turning off the "key presses repeat when key is held down" option under the keyboard settings, but this is not an acceptable solution in the long term.