Well, I'm still here! The rice and beans were boringly bland (simply because I didn't use much care in seasoning them), but not lethal. I had left the leftovers on the stove overnight (dozed off and forgot to put them in the refrigerator when they had cooled off) and put them in tupperware the next morning right before I left for work yesterday. I microwaved them a bit and had them for lunch, and didn't even get an upset stomach or the runs.
There is a logic for the concern: there's a range of temperatures between hot and cold that is just perfect for bacteria: they thrive in warm temeratures, while they either die or stop growing in food that's either hot or quite cool. I always thought this was more of a problem with eggs or meat, though... those foods can be food poisoning dynamite.
EDITED TO ADD: this was brown rice I ate Thursday and Friday, not white rice... although I don't know if there would be a difference between the two as far as food safety goes.