I would consider sitting on 100% cash right now much too risky! I hope you're referring to your trading position and that you have a core position as well.
If not, then that's the classic market timing error, and if the stock skyrockets straight up without going down first, you'll miss the entire runup. This is specifically how market timers do worse than buy-and-hold investors and indexers. They did studies on this. Market timers do worse by being out of the market during the big runups, since most of the rise in a stock will happen in a few big runups with stagnation in between. I can't remember the details, but it was something like, for most stocks which gained a lot, the gains over 5 years are typically concentrated in three specific one-month periods, so being out during one of those periods wrecks your gains.
I do have some money which will go in if the stock drops below $310, but I have never sold a share and I don't intend to so so until at least 2019. If it goes straight up I do well, if it dips and I can buy more and then it goes up I do better.
So many professional FUD'sters on SA. The Legion of Doom under a temporary truce.
