I use calculations whenever possible...sometimes modifying the image first to increase subject vs background contrast to make the calculations easier. Quick mask will sometimes do the trick. For really fine detail/really complicated work I've used third party software/plugins before such as FluidMask, but it's a resource hog and a pain in the ass to learn.
I use photoshop for the most part but i would also be interested in working with other software. Btw, can anyone recommend me some good online tutorials on this? That Ken Rockwell guy got me into this so now i have to look into it,lolz.