MB here. We have done a $1/hr raise for 3 years in a row. This started out being approximately a 7% raise and is now more like a 5% raise (as her salary increases the percentage decreases.)
It's starting to max us out and I don't know if we can sustain that annual increase for many more years, though we'd love to keep her for at least 2-3 more years.
My annual increases have always been in the 3-3.5 percent raise, when I got one (I don't always get them.)
Once we maxed out on the $1/hr raise, we offered benefits instead (health insurance, more vacation time, etc). It worked for us because our nanny's responsibilities decreased with preschool and kindergarten.
She is still with us.