Just got my first paycheck after my promotion last Friday and I'm taking home less money than before, due to maxing out my 401k percentage for the year! My take home pay is only ~$200 less biweekly, which would is only $5,200 less a year; but my 401k is getting $17,500 a year! I'm happy to take the cut and pay less taxes for the next X amount of years for that.
I also negotiated an extra $4,250 into my promotion raise! This year is turning out pretty badass for me, after a not-so-great start. :)