Mix and match (recyclables)

So have a look at this plastic carrier. Has a nice "Recyclable" sign, but the handles are re-inforced with cardboard. So:

1. What happens if you bung the plastic carrier in a plastics recycling bin? What happens when it gets to the recycling plant? Obviously there can't be some dude who stands there sorting through everything, and stripping paper bits from plastic bags? (same goes for those paper envelopes that have plastic windows)

2. Assuming plastic bags with paper are put into the plastics recycling bin, does the paper contaminate the plastics? And vice-versa? (of course, I'm well aware that there are plenty of idiots who throw all sorts of crap in recycling bins)

3. Should the conscientious recycler go to the trouble of removing paper bits from plastic carriers, and plastic windows from paper envelopes? Where does one draw the line? And how effective is being super conscientious anyway?

4. On that note.... here in Singapore we have all these recycling bins located in public places, and I'd go so far as to say probably 99% of them are "contaminated" with stuff that isn't supposed to be in there, e.g. food in the paper bin, paper in the plastic bin, plastic in the paper bin, etc. What happens once it gets to the plant? Is / can it be sorted? Are the efforts of the conscientious recycles thwarted by the actions of the careless?