"Good artist create, great artist steal."
This quote is thrown around a bit too much, without realizing the amazing difference between stealing and copying.
Stealing, for many, is same as copying, rip-off. Let me tell you a thing - Copying is NOT stealing. 
Recent case of Curebit ripping-off 37 Signals and other people's design in name of A/B testing and 'we are just a small startup' is Copying.
I recently saw Dell's copy of MacBook Pro. Trying so hard with aluminium body, almost same keyboard etc. Shameless, ripoff done without any thoughts. It's like you copy someone's website and don't even change the Google Analytics code. They couldn't see it wasn't aluminium body that made MacBooks what they are (in design) but the principle behind them. Apple did a better job of making MacBooks with plastic body than most other laptop makers.
When you replicate the outcome - it's a copy. And it, often, results in mediocre results. Nothing artistic.
Stealing, on other hand, takes much more. When you steal, you claim ownership. You replicate the process, the function, the principle.
What smart-phone did to wrist-watches is stealing. They replicated the functionality, the process from the original, and made it their own. What Apple did to Dieter Rams' design is stealing. They replicated the principles behind them.
Stealing is not easy. It takes balls and insights. It takes a great artist to steal. To go and copy how Google displays it's search result is one thing, but to understand why they do what they do and then replicate that is another.
Copying seldom harms the original. Since they just replicate outcomes. There must be a many copies of Mona Lisa, but original is unchallenged. Stealing, however, changes the game. Stealing the process and making it your own (read: improving on it) often challenges the original. In fact, it means to.
iCould was stolen from DropBox. Heck, at every iOS update, you could hear - so many startups were killed. Its nothing less than hijacking. Take it away, change it and own it.
You will often hear designers looking for inspiration. Some go and fetch visuals to copy. Others go and fetch ideas and solutions to copy. (I do both).
 Before this becomes a troll-feed and we start arguing about merits of dictionary definition, let me clarify I am talking about copying and stealing as two different concepts. You can title them whatever, I choose to title them stealing and copying.