A couple more notes on the biscuit cutter...
1. The biscuit and glue add moisture to a half-moon shaped area of the board. That part of the board expands slightly. If you sand as soon as the glue has set, you can get a flat joint at that point, but as the water from the glue dries, the wood will shrink and create a ghost of the biscuit. You should wait as much as a week for the wood to really dry around the biscuit before final sanding. (Same can be said about the joint itself without the biscuit, but a slight shrinkage along the glue line is less noticeable.
2. Like Allen I have a non-biscuit use for the biscuit cutter... I like to screw the tops to tables and cabinets through a tapered hole made with the Kreig jig. But where you attach the top cross grain (the ends of the table) you have to allow for expansion. The ugly Norm Abrams trick was to wiggle the drill while boring the hole. I just cut a biscuit slot where the hole comes through the apron. The side aprons can flex the small amount needed for the top to expand and contract, so I start the side holes slightly away from the end and make them without the biscuit slot.
3. I found that if I was absolutely careful - jointer held very tight to the reference face - I could get perfect alignment with the Porter Cable biscuit cutter. If I just went down the line quickly making the slots, the alignment was not as perfect.
4. While we are talking about edge jointing boards, the school technique is to run the edge of the board over the jointer, but jointers leave scallops. My (very fancy) saw with a glue-line blade cuts smooth and straight, but with tiny scratches from the saw teeth. So in either saw or jointer case, I do a couple passes with a jack plane (fairly long hand plane, but not as heavy as a jointer plane) to perfect the edge before gluing. After planing, before clamping, I sometimes check to see if a piece of paper will slide between the boards. If it can move, I do more planing.