First, I want to clarify something. There's the Arduino library, and the Arduino hardware.
I love the Arduino Library for quick programming. Easy to use, easy to remember function names, and a very easy to navigate online reference system. I love/hate the Arduino IDE (Processing IDE). It's simple to use, but is missing some features like line numbers running down a side, and you can't collapse functions like is Visual Studio.
The Arduino hardware is overpriced. I have only ever bought a few Arduino Pro mini's. Now I just always design and fab a board for whatever I want to do. That way I get exactly what I need for about the same price as buying an Arduino, not even considering what I'd pay in shields. Then I just flash the blank AVRs with the Arduino bootloader.