It occurs to me that this whole issue is sort of like Angel Policies - some stamp companies will let you sell what you make BY HAND (no mechanical reproduction), some won't. Some artists are okay with you selling the designs they originally came up with, some aren't.
I'll also say that I've seen MANY instances of several people having the same (or at least very similar) ideas at the same time - how do you determine if you truly were the FIRST? There have been several ideas that my friend mentioned to me or that my husband mentioned to me and a year or two later, that idea was being sold somewhere. For example, my husband had the idea for something like "Angie's List" about five years before that showed up, but had no idea how to bring it to fruition, so he did nothing with it. Angie had the same idea, but knew what to do with it, and she's everywhere now!
This DOES NOT apply to someone who has produced actual art (like DeeAnn) and has had it stolen - totally different deal there! Still, I agree with her assessment of how much it is really worth to pursue and prosecute the offender. Things like that need to be considered, for sure.
I had an instance of someone here on SCS not only saving one of my cards to her favorites, but pm-ing me for directions on how to make it (which I told her, including dimensions and step-by-step instructions). Imagine my surprise when it surfaced in her gallery, on her blog, and on the blog of a team she designs for - with no mention of my name at all! I debated saying anything, but decided to email and gently inquire if she could please at least mention where she got the idea. She was very gracious and apologetic about it and said that she honestly couldn't remember who she got the idea from (?), and that she would certainly correct the situation, which she did. Sometimes it really is an honest mistake, sometimes it's just a lack of communication, sometimes it's ignorance of how things should be done, and sometimes it's because they are just selfish and don't care. It's hard to judge which is the true case...
Happy for no reason...