In terms of how to check the wear on grinder blades. Experience and intuition are one measure - you just get to know by looking at the blades over and over, or you can use AM's suggestions. From a practical point, there is a simple test I like to apply (although it does consume a bit of coffee). Run the grinder for a few minutes using say +/- half a kilo of coffee (or less for smaller grinders). If it's getting hot and the smell of burnt coffee is evident, then you know the burrs are stuffed. This method is essentially relying upon emulating the practical duty cycle of a cafe during a busy period. Very few home grinders go through the volumes to worry about wear, except if you have somehow got hold of an ex-cafe grinder. For cafes, it's a numbers game and you are recommended to use conservative judgement - if in doubt, replace the burrs as it's a relatively cheap investment that greatly assists in producing excellent and more consistent coffee. I have a bad habit of lifting the doser chamber lid of cafe grinders and smelling the ground coffee. Seems my nose can't stay out of trouble.
