Last week, Matt Kloskowski on his blog Lightroom Killer Tips (which, by the way, is an excellent Lightroom resource. If you haven't been there yet ... What are you waiting for?) posted an article Is it wrong to steal Lightroom presets? discussing the ethics/legality/morality of copying someone else's presets and applying that to your own work.
With the exception of Matt's drug company argument (drug companies use patents to protect their drugs. It's only when the patents expire that others can produce generic copies) I have to agree with him. To equate the process with the final product is not something copyright law contemplates. It's ludicrous to think that Michaelangelo could sue because you happened to sculpt using marble because he used marble! You could give me all the marble you want and there's no way you'll get a David or a Pieta out of me! LOL
The point is that presets, like actions, tips, tricks, settings, gear, etc are all tools. Now you might be able to patent a tool or a process but you can't copyright them. Had Britain held a copyright to the English language they would be the wealthiest nation on earth just from the American royalty payments alone!
Matt's admonition to "Get Over It!" is right on point. Look at presets. Learn from them. Apply them to your images. Expand on the possibilities. As a community of artists we all grow through our association with each other and each other's methods. Whether newbie or advanced, hobbyist or pro, we each have things to contribute and learn.
All that being said, never confuse the process with the product. It is illegal and immoral and unethical to take another's work and pass it off as yours. This extends to using someone's photo as an ingredient in something you create. You must still get the permission of the copyright holder to directly use their work.