Sorry to put you on the defensive, Nik! No harm intended.
There are really gray areas, here. I wouldn't, for instance, make five booga bags and try to sell them in a consignment shop. I would take money from someone to make a booga bag especially for them because I would want to be paid for my time. I wouldn't tell anyone that I had designed the booga bag. I wouldn't try to pass off anyone else's design as my own. There are books that give basic patterns for mittens and sweaters, I would use them for reference and come up with my own design.
So Mer wants to make a square bottom bag. She looks at the monkey bag pattern and says "Oh, so that's how you shape that bag!" She proceeds to make a square bottom bag out of a material of her choosing, makes i-cord handles and duplicate stitches something on the side for decoration, she adds a loop and button closure and a pretty cotton lining, no monkeys or fun furs have been harmed in the process. Is that her design? I say yes. Even if it's the same size as the monkey bag.
DH and I have done a lot of research and discussion regarding patent law. You can't infringe on someone else's patent. If, however, you can improve on another person's process significantly, you can get a patent on your improvement. This is how I look at the knitting question. Be ethical, don't misrepresent your work.
Lionbrand has a pattern on their website to cover flip flop straps by crocheting with fun fur. The pattern is totally wrong. I figured out how to do it on my own (I posted a picture in the finished object thread). I have no qualms about selling them, because I didn't use their pattern. But I don't think anyone will want to buy them, so the point is moot and Lionbrand's lawyers don't have to call me.
Is anyone out there actually a lawyer? I am not a lawyer. You must proceed with your own best judgement and/or consultation with a real attorney. Twiggyann might be in family law. She can help me if Lionbrand tries to take my kids away.