[jakeinspace]

For personal projects, anything is fair game. Once you're actually distributing your program/library to users, I think attribution for any non-trivial/non-standard snippets or algorithms is a good look (just in the form of in-line comments, possibly in the header comment block). As long as the licensing works out (for example, GPLv3 snippet in GPLv3 project, or CC/MIT in a permissive open project), I see no problems there. Obviously, for closed source or otherwise restrictive software projects (especially when working for an employer), things get more complicated. While you won't likely get caught or called out for lifting a chunk of code off Stack Overflow (which I believe defaults to the MIT license), it's worth reconsidering.

But as far as looking for inspiration in other people's FOSS code? Morally that feels like very fair game. Again, attribution would be nice for an actual algorithm.