Design Ethics: Inspiration vs Plagiarism

I'm been wrestling with this question a lot lately: when does inspiration become stealing?

Here is my creative process in a nutshell:
1. Outline the parameters of the project
2. Research
3. Design concepts
4. Client feedback
5. Revisions (repeat as needed)
6. Finalize

Somewhere between #2 and #3, there is a line. On one side is "originality" and on the other is "been done." I've heard many times that design is really the art of taking ideas, using them and passing them off as your own. Are there really any new ideas? New to the context in question or the combination in which they are used, definitely. But really NEW?

As a designer, I am constantly aware of my visual environment. Part of that includes what is happening right now in the brains of other designers and what is getting published - i.e. trends. And what is a design trend but using the same idea and executing it differently or to convey a different message?

I try to be as original as possible, pulling things from my brain which has collected so much visual information that what comes out is an expression of many, many combined ideas. Even if it is inspired by things that are specific, what I create is new... I hope. Or as new as possible.

There are certainly lines I have been asked to cross and will not, such as slapping a logo on something without permission, using copyrighted images without paying for them or without permission, searching Google Images for a design I like and blatantly copying it.

But I feel as though the line is fuzzy... and for some designers I know, non-existent.

Thoughts?

For more "inspiration" on this topic, check out this blog.