Amen! I gave five months notice and am really regretting it. I'm a few weeks out and NOW they are saying "oh $hit she's leaving. How do you do your job again?"
This is exactly why I only gave 30 days’ notice as required by my employment contract. Other senior execs who left gave 1-2 years notice and either didn’t get replaced until the last moment anyway, or had someone “in training” for over a year. I left everything well documented and while I refused a consulting contract, I did offer to be available for free on a limited basis for questions. Only got a couple of calls, easily and quickly handled, because my staff was well trained to step up. So glad I didn’t give in for a longer notice period!