I use them as few times as possible. I much prefer the USPS, not only because I think it's the best service money can buy, (I have lived overseas and am VERY familiar with other governments' postal services) and it's the cheapest one as well.
I always buy insurance. Usually $50.00 worth, but sometimes lots more. I always buy delivery confirmation. Not that I don't think it will get to where I want it to go, but because I believe the thirty five cents helps the Post Office and I can afford it.