I also sometimes use the CT polyester cones, but even though I'm not sure I believe it makes a difference I still hear my grandmother telling me to never use polyester thread on cotton fabrics so I don't quite feel right doing it.
The myth that poly thread is bad for cotton has been disproved many times.
There are three different types of poly thread, filament, spun, and tribal. When someone has a problem with poly thread, it's probably because they are using the wrong type for the job they are doing.