It's a complicated question, only because there are so many types of plastics. There's what we call the plastics pyramid, where polyvinyl chloride—PVC—and polycarbonate plastics are considered the worst ones. So if you're seeing a three or a seven, that's where you're worried about chemicals. The seven is the polycarbonates that have bisphenol A, and the PVC tends to have phthalates such as DHP. There's less concern at the moment about ones and twos that you might find on a pop bottle.
On March 20th, 2007. See this statement in context.