I second that. R is terribly useful for the wide variety of libraries available and esoteric statistical procedures. But you would *never* want to write a long/complex program in R.

As you say, it's most convenient to work in some other language that's actually designed to be scaleable, object-oriented, and easy to debug. It's usually straightforward to call R libraries when you need them. I find that python+scipy+rpy is an almost ideal environment for day to day scientific programming.

Yes, and if everyone was perfectly rational, the market would be completely efficient and we would live in a utopia. In the real world, sudden price drops in small companies trigger panic-selling. Investors often move with the herd-- they don't have time to do all the research into a company's fundamentals and make an independent evaluation of a stocks worth. When there is a sudden price drop, all the think is "damn, better cut my losses now, because all these other guys now something is wrong with this company."

There should be regulation to make it exceedingly difficult to trigger panics by naked short-selling. Regular short-selling isn't so bad.