I dipped my toe in at $12, thought I was probably gonna get hosed, saw it skyrocket, then bought 25 BTC at $43 and just knew I was probably making a mistake, but now it's at $65. In theory, it should probably dip a little before the next time it shoots up, but it could also just keep rising to $100. If you have the time, I'd just watch the markets closely to see if it starts dipping a bit and get in if it goes down to $57 or so. If it goes above $68 tho, I wouldn't wait any longer. If you don't have the time to keep an eye on bitcoinity for hours in the background, you might as well take the plunge now.

Just don't invest more than you can afford to lose, in case things sour.