Well, SM-7 is so good at so many things, that it is often overlooked as a live mic. It rocks on stage! I have mics that suit my voice better for recording, but I have found it useful on any source that you would stick a dynamic on. Its performance through a PA I had not expected- Zowie!
i know this is kinda changing the topic, but i like the sennheiser md421 on vocals too. i've used the sm7,sm7b, and md421 and i liked them all on vocals and couldn't hear any difference between the sm7 and sm7b (i expected them to sound a little different so it was kind of shocking to me).
i think maybe i just prefer dynamic mics on vocals.