Am pondering this one due to Imogen's current early morning singing habit!
With Archie, I can never remember having the monitor on in his room overnight. Once we moved him to his own room we left his door and our door open, so any noises could be heard easily. He was always very capable of shouting loud enough if he needed anything 
It's been a bit different with Immy. She's always been such a quiet little thing - not a shouter - so the monitor is left on overnight so we can respond to any grumbling/upsetness. Also, being number 2 child, we need to keep her door closed so that Archie isn't disturbed. She sleeps beautifully now (11 months) - she settles like a dream and I cannot remember the last time I needed to get up to her in the night. However, she is going through a habit, and I'm sure the lighter mornings aren't helping, of waking at 5.45am and singing/talking to herself. I'm awake from that point onwards. She doesn't cry out for anyone and is quite content, but is bloody noisy, even with the monitor down at lowest levels. I'm starting to think about turning the monitor off, maybe just in the early mornings, but not sure whether it's the right thing to do.
Can you tell me what time you stopped the overnight monitor with your LO/s and why you made the decision to stop.
Thanks x
Archie Benjamin - January 2007
Imogen Sophie - April 2009