I got curious about temperatures and polyester thread melting, so I used my friend "google" and if we can trust the information, here are two links. One says polyester thread sticks at 440 degrees and melts at 483 degrees. The second link says an iron gets up to 400 for cotton and the polyester setting gets it up to 300 degrees. Seems like with a little care, it would be possible to use polyester thread and it not get sticky or melt.
http://www.thethreadexchange.com/miv...ad-information
http://laundry.about.com/od/ironing/a/irontemp.htm
Of course, this doesn't address the issue some of us have of using polyester on cotton that will it eventually break down the cotton, and personal preference trumps all.
I don't ever remember being told to clean out the bobbin when I learned to sew all those years ago, in 6th grade on a treadle. I do remember bringing my machine in every year to be "serviced" even when nothing seemed wrong with it. Probably to clean out the lint I never worried about.