Yep, it exists!
An 11/12 week baby growth spurt definitely exists and we JUST went through it.. here are some things I observed and took from it..
Monroe was MUCH more hungry, much more often.. so to remedy this, we fed him on demand, whenever he seemed hungry.. normally he goes 3 hours between feedings but we found that during this 48 hour growth spurt he needed food sometimes every 2 hours.. wish granted Monroe!
We also noticed he snoozed longer and harder.. post a feeding, he would conk out and snooze hard.. we didn't wake him and didn't worry about his routine as much these few days.. we let his sleep be as important as eating, as that's when SO much growth and development is happening!
I also noticed the babe picked up new skills.. he seemed more alert, able to notice objects to much more, much more vocal and could GRAB things, yes grab and hold things.. yahoo!
Hooray for growth spurts I say.. this one wasn't so bad for us :)