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
I'm not a web developer, but I might have some insight that will help as well. My team has created several applications that have served as the starting point for other applications delivered to various customers.
The successful derivatives were those in which the developers took the time to learn the architecture and why things were the way they were. They then took the more crusty parts and rewrote them and in general expanded and improved the architecture.
Invariably, when a team simply took the existing project and tried to 'brand it' or copy it for a customer without actually figuring out the systems, they either created poor implementations of the extensions or had the project fail outright.
I realize this is a bit off the main topic of the ethical issues address by others here just fine, but my bottom line is that pure theft usually costs you more time than it saves.
This is how a lot of design is accomplished. Except it's obscured by lots of lifts, not a single wholesale lift.
For the most part, ideas are fine to take and implement. If people couldn't take existing ideas and expand them or re-implement them, we'd never have gotten out of the dark ages.
If you feel the need to steal code because you can't code HTML/CSS well or don't have an eye for design, steal from a place that explicitly permits you to use their design/code, like OSWD. In general, stealing HTML is fine, but ripping off CSS wholesale is a no-no. Just because you can easily view the CSS source doesn't mean that it's ok to just copy and paste it.
Don't steal graphics, period. Especially things like photos and logos and icons. If you need that sort of thing, purchase stock photography or take your own photos.
When in doubt, ask the owner of the site.
Oh, this is a hard question.
On the one hand stealing is wrong, on the other hand you are obliged to save you employer money by solving a task quickly.
My only advice is: If it feels wrong in your gut, you probably stole too much.
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.
Stealing code or designs is immoral and in some cases illegal.
Taking inspiration or copying functionality is less of a problem. For example, at some point in time someone realized that putting a "Forgot Password?" link next to all login forms is a good idea, now everyone does it. It's not theft it's just replicating a good idea.