1) Nepenthe is too vague. Accelerate sleeps whomever is affected by it when moves hit 0. If you are fighting you may mitigate this but say you cast it on someone who does a lot of running away from you...

2) Correct me if I'm mistaken, but the other drawback to Petrify Flesh on yourself is that you can't have it up and flight at the same time. As Nepenthe said though, I still found uses for it and it's situationally really nice to have (also used offensely to keep someone from flying).

3) Buoyancy can be mean combined with summon (offensively) where you can make someone buoyant so they are thrown into the next room if they can't escape before you hit them. Knocking people into Centurions is one of the more devious things I've seen done with this.

That's pretty much it.