I used it a couple of times. The first time was when my son was little, and I found a really great and affordable sitter. The second time, all the sitters in my area were asking for $20+ an hour (one woman was actually requesting $50/hr). Personally, unless I see a degree in child care, I'm not paying someone that kind of money to sit in my house, play with my kids, watch my TV, eat my food, and leave a sink full of dishes for me to wash.
I haven't used it for one but I am a nanny and am on there(: it's a great sight! I have gotten several jobs off there and they background check all the nannies and families can review their experience with a particular nanny on there as well.