My best: Buying Apple (AAPL) in '98 or '99 when it was hovering around $14/share. I was single, back in Germany after six months in Bosnia, and had cash to invest. Having being an Apple person since the IIe, I decided to invest in what I believed in. My only regret is not buying a lot more. My worst: MolyCorp (MCP). A few years ago, the tech press was filled with dire warnings because China was the sole provider of the world's rare earth minerals and was using them for political leverage. When MolyCorp re-opened their Mountain Pass mine in California, I figured a domestic source of rare earths was a cinch. How could this not be a great investment? I bought a chunk at $11/share; this morning, it reached $2.82/share. I don't think I'm going to be a hedge fund billionaire any time soon.