"If you have to make cuts, you really want do it once, all at the same time, and then put it behind you."
I'm fairly sure that's what Yahoo did at the end of 2008 in their "Get Fit" exercise. We were told that the cuts would be severe so they would not have to go through this ever again.
And I think this is now the fourth layoff since that "layoff-to-end-all-layoffs". I hear rumours that they are already scheduling another round of layoffs in engineering later this year, somewhere near September/October.