I have my own eyes, frequently observing whole floors of empty desks (85-90 percent) - all assigned to employed but absent employees of Los Angeles County. As for the same abuse among Federal employees... here are just of few of the links to stories about government employees paid to sit at home, or have fun doing anything they want to...:
Link 1, Link 2, Link 3, Link 4, Link 4, Link 5.
Indeed the number of featherbedding government workers in both federal and state government are enormous - as to the total number of such, I found no 'total number' estimated... but from simple observation, I would deduce that the number may be as high as 40% at the federal level, and likely higher than that at all too many county and state government agencies - that deduction based on simple long-term observation.