Brent, just watched a show "Ron Hazelton's House Calls" and he had a concrete countertop made for his bathroom. They used the melamine (sp?) covered chip board so that made a nice finish for the top of the counter. He used pink insulation and glued that in the middle for the center cut out for the sink, he wrapped the edges of the pink insulation with clear packing tape, said it gave a nicer finished edge. Using a chrome pipe he cut the cut outs for the hot/cold and faucet and glued those round pieces onto the board after wrapping with clear packing tape. He claimed he developed an added ingredient to make it stronger than normal (hype to buy his???) anyway, he mixed all ingredients thoroughly dry then added water. He filled the mold 2/3's of the way, had a piece of woven fence (for strength) as well as a couple pieces of rebar, then the interesting thing, he used a random orbital sander on the bottom of the melamine board, running it across the bottom, it was magic the way it transformed the concrete as well as vibrated the metal into the center (to much and it would be on the top when done!). Anyway, other tips, he let it cure in his shop in the mold for a week, then he polished it once out of the mold with hand stones of different grits. Then a clear sealer so it didn't absorb or stain. Looked very nice against the natural tiles he had in the bathroom already. I still have the show on my DVR, if you need anything more specific, I can recheck it for you and find out. Hope this helps. Oh, he ran the ROS under it before putting in the wire mesh and rebar so he could take his time and get it leveling and looking nice (this is the bottom) then he just laid the metal on top and not long it disappeared!
I also forgot, he made the form from the melamine chip board, put silicone in all the corners and sprayed it with a solvent of some kind so he could press and make the silicone a half round with his finger (solvent kept it from sticking to his finger) and this insured a rounded, finished edge as it is sitting upside down when in the form.