As our kids b/room are at the other end of the house, I stopped using it for DS when he was about 12-14mo after forgetting to turn it on one night and waking up hearing him cying so I figured that my ears were so well trained by then I'd be able to hear by myself.

We are still using a monitor now in DD's room but only so that I can get to her asap when she wakes in the night so she wont wake DS at the same time.

All comes down to how your house is layed out really and what level of peace of mind you need to be able to relax to sleep.