I used shadowmeld in Arena to delay the usual "Kill the Hunter" first bit. It also let me see where best to attack from as the enemy formed up. Our team did better when our NE hunters were stealthed to start. Of course, this may only have been a benefit in the lower rankings.
I used it a lot on a PvP server to hide from corpse campers: rez in a bush and immediately hit shadowmeld. They'd get bored and move on. When I learned to eat and THEN hit shadowmeld, I could heal while watching them look for me. It was rather funny.
I rarely use it in Raiding but I do use it if I FD out of a 'wipe' and I need to hide from a pat or something. So, it's not useless but mostly so.
PvP has use, PvE... not so useful: very conditional!
I never got a dwarf Alt high enough to use Stoneform much.