carroll, another view...
Grinding whole cloves in a coffee grinder, or even in a food processor, so dulls the blade that it's just not worth it. The cost of blade sharpening, or even replacement, far outweighs the cost savings over simply buying cloves in the ground form. Also, each time I buy whole cloves at my favorite herb/spice supplier (at the holidays to make pomanders of citrus fruits), they make a point of saying not to grind them at home but to let them do it with the bigger equipment they have (citing specifically how tough cloves are).
As for powdered sugar, I've tried it, and I never got the evenly powdery texture of commercially available powdered sugar. I got something closer to superfine sugar. Also, powdered sugar has a bit of cornstarch mixed in, reportedly to prevent clumping. Depending on what your use is for it, homeground might work for you, for me it didn't and I needed the even texture of the commercially made.