I find myself doing this a fair amount, but there's clearly a point where you have gone too far. I consider decompiling someone else's code too far, along with taking assets that aren't yours, unless you have approval to do so. What about the developer's blog, if there is one? Surely there are other cases I haven't covered? Interested in hearing your thoughts.





I think being inspired by other's work totally okay, especially when there is a permissive license. Of course, you should always follow explicit rules.
In terms of ideas and inspiration, I don't think anything is off limits. It becomes "plagiarism" when you rip something off "word for word". Just like in school projects, you're told to "write it in your own words". So you should modify your inspirations as to take your own twist on it.