I still have the issue with a new 17 rmbp and 10.8.4. Two external monitors on two Apple TB to DVI adaptors. About 50% of the time one of the external monitors will not wake up from sleep eventhough the computer still thinks it has 3 displays. Unplugging and replugging the adaptor will not awaken the monitor, and I have to reboot to make it awaken.
Don't know if I mentioned my solution in this forum or another, but I used to have this problem on a regular basis with external Dell monitors, I solved the problem by going into the Energy Saver control panel and turn off (uncheck) the option to "put hard disk to sleep when possible". Everything else was left at the default settings for Battery and Power Adapter settings.