ARtrvlr Has it right the 30degrees produces a finer "sharper but more fragile edge. The 40degrees is almost as sharp and doesn't slice quiet as well but is more robust.
So my edc folders and small fixed ( eg the parer and fillet knife in the kitchen) are sharpened with the steeper sharper 30degree edge.
The machetes axes and cleavers are done on the 40 degrees. AND the kitchen knife my wife prefers to use. In short those knife prone to more abuse.LOL
Be aware there are three ways to stop the Spyderco from working at it's best.
#1, skip on the first grind/profile with the corners of the grey stones. You must make sure you have fully reprofiled when you first the 204 ( reprofiling is to ensure the angle you are putting on the edge now matches the angle the stones you are using). One of the easier ways to ensure that is with a Sharpie and a magnifying Glass ( yep I've hit 40) colour in the edge of the knife 2-3mm in for the full length. One stroke on the sharpmaker, then inspect. The stones will remove the black Sharpie mark where they are contacting, if you have black on the edge side of the bright mark made by the rod you need to put it back on the rods till you can give it a colour and a wipe and it removes the sharpie mark the full length of the edge. Do not skip on this bit the first time you put a a blade on the Sharpmaker or if you decide to change the angle. But you shouldn't need to reprofile every time you re-sharpen. Don't rush it, take your time.
2# Not keeping the stones clean. It is amazing how well things work when they are clean/maintained.
3#Sit down with a root beer and watch the dvd from start to finish. Amazing how well things work when you follow the instructions. When you have gotten comfortable with the "right" way to use it then you can start mucking around and "freelancing".
An amazingly insightful look at the Spyderco 204, from one of the best looking blokes on the net. RATFLMAO
http://www.youtube.com/watch?v=6yVN9lLVPM4
Carl