Plagiarism is defined as knowingly promoting the work of others as your own. Generally we do not do this, and while ideas may be reused or built upon, most modern works are truly innovative. Here are a few examples from various fields:
Micro-identification dots (as used by Yamaha)
High capacity air freight (Boeing? Airbus?)
Sattelite guided missles
Personal locating and/or signalling devices
True variable valve technology for motorcycles (as opposed to F1 cars)
'Big Bang' cranks (on roadbikes, not Doohan's NSR500)
I could go on and on with this, but there is little point. Ideas and designs may be improved upon or regenerated, but this is far from plagiarism, and good design is much more than 'well though out plagiarism'.
Good design is innovative and adept at performing the task for which it was meant. It is also often robust, reliable, simplified, aesthetically pleasing, and cost effective. I value all these things and this, for me, is what good design is.
- boingk