I refuse to ever buy it again until it drops to the $3s.
Here's some advice that works for me. Keep in mind I started Bitcoining right after the Mt. Gox crash and I've done quite nicely since.
This is a "safe" method that won't make you $ every day, but when you do profit, you profit rather nicely.
Keep an eye on your exchange's charts and place a buy order for almost all of your USD $.50-$1 below the current price. Keep your bids on psychological barriers (e.g. $4, $4.50, $5, $5.50,) but add another penny or 2 (e.g. $4.02, $4.52, $5.02, $5.52). At some point, especially if you use Mt. Gox or TradeHill, someone will come along and dump a few hundred/thousand coins all at once.
If your buy order is large enough, the market will bounce off your buy order and within 5-10 minutes it'll be right back where it was. Then you sell everything (or, if you're feeling lucky, hold onto them if you think the market will continue to go up). Then repeat. This little technique usually earns a profit close to 10% of total holdings on every trade.
The one thing to be careful of is the removal of very large buy-walls or HUGE sell-offs. For this reason, I'll usually stick my bids 50 cents below current price during the day and $1 below when I sleep. But, I've had several mornings where I've woken up and been like "HELLLL YEAHHH!" It's a great way to start the day.
Edit: I don't try to hit the peaks and valleys...I AM the peaks and valleys...sometimes. This is all very generalized but you get the idea.