This discussion interests me because I'm a DoD Federal employee myself. Here are a few questions/comments I have after reading this thread:
1. 100K is our average pay?? Really? That'd be a mid GS-13 and certainly within my organization the average GS grade is well below that. Now if you're including paid benefits, then maybe that is correct, but that'd be highly misleading to do that given that most individuals in higher-end private sector jobs wouldn't add up the value of their benefits package either and include that when they mentioned their salary for comparison.
2. I'm a little surprised that I sensed more of a negative tone than a positive one from the federal workers who posted so far. Being somewhat Mustachian myself, I'm getting rather excited about getting to work one less day a week, and am hardly disturbed at the prospects of being paid 20% less. We're getting an equal trade of precious time for that 20%! There is nothing more valuable than time to a true mustachian, right?!? Since congress broke the ice on this whole 4-day-per-week workweek, I might see if I can build up the nerve to ask for that arrangement permanently!
3. As for my organization specifically and my department, we're thinking we can absorb the 8% hit without the need for furloughs because we've been pretty conservative with our money so far. However, as I understand it, we'd have to get special permission to not furlough regardless of whether we can afford not to do it. Again, I'm a bit conflicted on that, because even though I'd welcome the extra time, I know many of my fellow non-mustachian co-workers would be devastated by the pay cut.
4. I haven't seen one of those letters yet that show that it's an actual 26-30% pay cut if you include the cost of the benefits, but are they including the reduction in federal and state taxes in that? For my specific combined state and federal marginal tax rate, that'd be 32% less tax on that extra money I would no longer owe. So my point is, you may have fixed benefit expenses but your tax "expense" should go down quite a bit.