Making sense of numbered plastics: Good, bad and ugly
THE GOOD: The numbers on recyclable plastics don't necessarily mean that the plastic can be recycled now. They only indicate what resins are used. Markets for #1 and #2 bottles and #5 cartons are pretty good these days; the others, not so much. So choose those plastics over, say, milk in cartons or soy milk in shelf-stable boxes.
BTW, when I was at Sedona Recycles, I learned that you should leave the caps on plastic bottles because they can be recovered by the processor in their stage of the process.
Trex recycling poster: What they accept
No matter what the number, don't put plastic bags or films (like the plastic pillow packaging) in with the rest of your recycling because it messes up the machines. Many groceries can accept film plastic with their produce bags (although they don't advertise the fact because they don't want to be swamped; so be respectful). Ask your grocery where they send their bags. Many send them to Trex to make plastic lumber and if so, can find out what Trex can accept here.
THE BAD: If you want to learn more about what's wrong with the other numbered plastics and why you shouldn't include them in your recycling (unless your recycling service specifically says to), this New York Times article explains.
THE UGLY: Surprisingly, according to the article, #3 (PVC) is the real bad guy, even more so than #7 which is the miscellaneous "Other" plastic.