What are the milestones that make life easier? What's your experience??

Your baby sleeping through the night is the the best milestone. Sleep deprivation is the worst thing when you have a baby. (I appreciate that not all new parents get to sleep through the night for months or even years).
Feeding themselves when more than 50% ends up in their mouth and not on them, around them, on the cat etc..
Toilet training - rather obvious but great to go out for the day without a huge bag of equipment and worrying if there is a baby changing room.

I noticed that other mothers started to look different a couple of years after their children started school and gradually worked out that it is around the age of seven that one escapes the 'black hole of motherhood'.

I take no credit for that phrase by the way, it was invented by a marketing research company (possibly the Henley Centre) - they believe that 'mothers' disappear off the purchasing ladder for about 10 years in terms of personal purchases. What a loss to the economy!!