Linux (OpenJDK 1.7.0_17)
No EXP bar is present on my Ubuntu 13.04 machine when playing survival mode with the 13w16a snapshot. Launcher's not throwing any exceptions that I can see that would be related to the problem (only a rather trivial FileNotFoundException because a 1.6 data file isn't ready yet). Incidentally, an option to keep the launcher open would be lovely, as we can give you the stack traces for our builds).
It's also not showing any EXP orbs when mining or killing chickens, though the sound of the orbs being picked up is still playing for me.
MC-13592 XP bar missing