If you want to display it or sell it, get permission. Most "serious" quilt shows will actually ask if you have used a commercial pattern and require you to obtain written permission to display a quilt made from that pattern. I have had letters from people to that effect when they made a quilt from a pattern on my website.
Copyright law is a very interesting and complicated issue. Ebay has a HUGE problem with it! If you look up "custom boutique" little girls clothing, you will see literally HUNDREDS of Disney, Dora the Explorer, Hello Kitty, and other "character" outfits. And, unfortunately for the honest designers, those are the ones that sell for hundreds of dollars. I would never make one to sell. If I want to make my granddaughter a Minnie Mouse costume, however, I am not going to feel that I need to write Disney to get permission.