Here is my take and what I think in a nutshell. (Yes, my brain is so tiny it can fit in there too.) If I am wrong please correct me, I want to understand this.
As long as you are not SELLING a quilt, a bag, etc. that you have purchased the pattern for it's okay. And you can sell such items if the pattern maker is alright with it. But if the pattern maker states that you cannot sell items you make from their patterns, that is covered under copyright.
If you use a pattern and enter a quilt in a show, it depends upon the venue whether or not they require you to specify whose pattern you are using. I would think it would be obviously wrong to claim someone else's pattern as your own. But making a quilt from a pattern and showing it is okay.
Where am I right/wrong?