I have one, but I've never tried it on vocals. It is a fairly flat/accurate mic and I imagine it would require a great singer in a good sounding room to pull it off. Probably great for opera and choir distance miking. For close miking of a single singer, be sure to use a pop filter and give it a go.
I once played guitar for a southern gospel quartet who used SM81's on vocals. They also had 2 Peavey Black Widow subs in their PA system. The bass singer's voice sounded like the voice of God through them.
I have also recorded vocals myself with an '81. A pop filter is a must unless you're distance miking. They are very prone to popping on vocals. But they can sound quite good.
awesome, thanks a lot everybody. ill try it out as soon as i get mine in the mail. i was going to buy a ksm27 too, but if these suffice for vocals ill hold off for now and save up for a ksm32 or 44 instead. i actually got a pair of old sm81s off of ebay for 300$. they were pretty scratched up cosmetically but the seller seemed highly reputable and assured me that there were no problems aside from the bevy of scratches.