When MtGox goes back up you're going to a surge in volume at other exchanges. Think about how many big guys had in storage at MtGox before they lost most users trust...
Sure. People will move their coins elsewhere. Why sell 'em though, unless you've lost faith in BTC rather than gox? Bitcoin wasn't hacked, Gox was. (so goes the story anyway. Whether or not you believe it is up to you).
If one had to sell to withdraw from gox, then I could understand. But when you can just click and transfer back to your wallet...selling doesn't seem particularly intelligent to me, especially when so many other people are going to try to sell too and you won't get your value.