I've noticed this before todays patch,
About 6 out of 10 tries, the launcher never loads when you press Play from Steam.
Steam loads the menu asking which launcher to use, "Play DayZ, Run Client" Selecting Play DayZ (honestly, not sure why I'd ever use the other one as it doesn't work for modded servers.)
Nothing happens.
DayZLauncher32.exe is displayed in Task manager. Must force close from Task manager to get the launcher to launch.
I haven't tested more than once on todays patch, so maybe this was fixed today.