While designing my site I am constantly faced with the issue of whether its ok to TAKE ideas and designs from other sites. In some cases there is no distinction in certain aspec
Stealing resources (graphics, code) is not really OK if they're not specifically marked as free/open/creative-commons/etc. Stealing design and layout is a bit sketchy if you're just xeroxing the same layout using your own code -- using someone else's design as a starting point is one thing, but don't just recreate their design verbatim. Stealing snippets of code for specific bits of functionality is fine (IMHO) since even if you grabbed a reference manual to learn it from scratch you'd end up with the same thing. (Think: javascript for changing an button image on mouse-hover)
Having said all that, imitation is the sincerest form of flattery. Don't steal resources, but using other sites as "influence" should be OK. Or, if in doubt, ask the owner of the site you intend to use as reference/influence.