Thats a funny coincidence. Starting a french drain project tomorrow. Not using the sock on the pipe, but we are using filter fabric to line the ditch and cover the rock. Toping with new fresh topsoil for seeding or sod (home owner to finish). Agree with Ron, if at all possible don't put dirt on top. They actually work great when the water can get down to the pipe!
I've researched pricing for drains on here. Some guys were saying $10-15 a foot. I don't see how they can do it so cheap. I'm leaving dirt on site, regrading another area, and it's still $20-25 a foot. Guess it all depends on labor costs, depth and finishing touches?