I confess I've been totally confused by the amount, radius and threshold parameters of unsharp mask 'sharpening' - that is, until now, after coming across this wonderful explanation:

http://194.100.88.243/petteri/pont/Photography_lessons/ppc_Lesson_2/_Sharpening.html

Note - for point and shoot cameras this doesn't mean a lot because they do tons of sharpening in the camera itself.

Enjoy.

Thanks for the site - there is a lot of good information in there!