These services are indeed legal; they are just very, very expensive. I think you'd only use them if you were in a total bind. My sister used one when she unexpectedly had international travel plan's with about a week's notice; her youngest kid did not yet have a passport. With a full-time job and three young children, there wasn't any way she could stand in line all day at the local passport office, so she had to use an expeditor.

Made me realize I should get my baby a passport just in case.