ok first off i've never done one...duh....but............
i'd love to see someone do a coil sprung sas but like rob said, if u think about it, the leafs are much more forgivin in allowin you to not have to worry so much about extra links, if u get those links wrong on a coil....it's gonna suck! coils could pop out, it's gonna be wicked bad! but hey man, if you're good in math and wanna do some h/w go for the gold!!! get something that will flex like your rear set-up!