"Correct me if I am wrong. However, I seem to remember that Ken Lay purchased Enron stock as it was in its death spiral. "
Years ago I bought stock in a company with depressed stock, mainly because the new CEO bought a bunch of stock. The result: I got burned, the company almost went banckrupt! The company was Data Dimensions.
The moral of the story is, yes, it is a positive thing if the CEO buys stock of the company, but it is far from being the magic signal that the stock has reached its bottom.
I don't recall that one, but i've seen others. For example, the founder of AOL bought 1 million shares at around 25 on the down slope from 100. I think he wanted to rally his troops. This definitely had an effect on investors and traders, but only for a few days. I've seen such buying by CEOs or board chairs often enough that i don't think its meaningful. To be meaningful, you need to see more insiders buying more shares.