I think I'm selling mine when they go under 400$, which I hope will never happen, but might even happen today the way it's going down now.
On the other side I think I will sell them at around 900$
I sell my coins when I need cash. And that is only reason, in last two months I earned more money on bitcoins then on my work. So when I'm short with cash I sell some coins until I receive my salary. My passion is gambling so I use my coins for that mostly, and some part in several alt coins, and for trading.
I will sell them when I neex cash, no matter how much is price ( higher price is better of course ). I like stable price, so spikes are nice to see and who knows make profit from it, I'm in different story.