One thing I learned during the dot-bomb era is think hard about holding too much of your company's stock and, especially, think really hard about exercising options and then not selling. Fortunately the stock drifted back up a ways over time and then my former company was acquired for a nice spike. So between that and tax loss offsets, I didn't do that bad. But I've been careful since. (Of course, more recently, I'd have been better off holding more for longer but I can't really complain.)