CharlieDelta - to answer your question with respect to the 'average' private pilot scene (i.e. not 2 crew ops as some have discussed). In my (limited) experience, it's not prevalent, but there are more than you would think out there. I would probably characterise it as an unsafe attitude, rather than unconcious incompetance.
They're generally perfectly capable of, and may even fly as a model pilot when an instructor is present, or they are being checked up on, but when they are not, either can't be bothered to, or don't feel they need to do the job properly, engage in questionable activity etc. Generally it leads to errosion of margins, and one day something comes along that surprises them, and they're way behind where they need to be.
It's an easy place to get into - the human animal isn't good at judging risk - we tend to work along the lines of "first time scary, 50th time it didn't kill me, so it must be safe". I've heard said that from 100-300hours (I think) is the most dangerous time of a pilot's life; you know enough to feel comfortable, and get yourself into trouble, but don't have the experience to get out
