Everything is a trade-off between security and convenience. For my largest holdings, I personally keep a paper wallet (printed sheet of paper with my addresses and keys) as well as a Flash drive with either the same in PDF or a copy/backup of the actual wallet.dat or whatever it happens to be. I do have a tiny bit of coins on exchanges, so that I can speculate a bit when the markets are fluctuating. However, it's nothing I can't afford to lose. I keep up with the value of my holdings separately using MyCoinBag.
RE: Most Bitcoiners Leave their Bitcoin At Risk