I hand lay my turnouts, but for regular track, I go pre-made (mostly flex track).
As for the Homasote, I have a 1/2" thick 4'x4' section that I used as a base for my O scale 'round-the-Christmas-Tree train that had gotten wet in a basement flood. I decided to try cutting it up into roadbed for the HO train. I got ONE STRIP completed and couldn't believe the amount of dust I had created all over me, my driveway, in my garage and my neighbor's yard (it was a windy day). My results weren't as good as I had hoped, but I figure the strip can still be used. For the most part, though, I think I'll stick with cork.
As for FINDING Homasote... Most of the big box stores carry it around here (Northeastern US), but I challenge you to find even one associate at the store who has ever even heard of it, knows what it is or where to find it in their store. It's a fantastic product, though, for certain projects.