One of the things I see is a general sense of "Join the party", which is nonexistent elsewhere. One thought I've had about the new Forum design is that "Bar Sport" and the Exhibition sections are now located DOWN, where you have to scroll down and look for them. I know it's just a kind of silly observation, but I think I'd like to see those two as the FIRST and FEATURED sections of the forum. It's what Arduino is really about after all, isn't it? Philosopically, I'd like to see the Community section at the top!
The hardware and software/IDE simplify development to the point where a complete novice has a fighting chance of actually getting a project working.. 99% of users are never going to see or care about register level code, assembler, and code optimization. They want something that can take simple directives and produce simple outcomes. Arduino delivers that in spades. I compare it to ROM BASIC that many early PC's had.. but at least it is compiled. The comparison is that it allows a beginner (remember what BASIC stands for? Beginner's All-purpose Symbolic Instruction Code..) to produce a usable outcome, even if that outcome isn't produced in the ideal way. For many real-world developers, especially hobbyists, a simplified coding scheme like BASIC or Arduino (Processing) allows non-professionals (like myself) to achieve goals that would otherwise just be discarded as "too complex". A good example was my Spectrum analyzer with video project. I MIGHT have been able to build and program that project from the ground up given enough time, but the simple fact is, I wouldn't have- this is a hobby for me, and the PITA level would exceed the amusement factor of the outcome. Arduino made it possible to put it together in a few hours, making it a reasonable time and effort investment. If the measure is actual real-world working outcomes, Arduino can't be beat.
I have AVR Studio loaded. I have built exactly ONE project in it, after the ungodly nightmare of installing it in the first place. I did a glorified version of Blink, and to be honest, I would walk away from microcontrollers as a hobby if presented with that. The "Examples" tab in the IDE of Arduino is such a godsend alone to new developers.. how many times have your projects started with loading an "Example" and using that as a skeleton? Nothing like an easy reference to working code.
However, as you note- it's really the people here that make it shine. Arrogance just doesn't fit in, there's not a feeling of one-up-manship that I've ever seen. This is quite a contrast to other microcontroller development sites, in particular those directed at Atmel's AVR product line.. in fact, what was once the primary technical resource is now little more than a Weenie and Flamer cookout.. happily, the Arduino community attracted the actual talent and knowledgable folks as the rats took over that sinking ship.
I'm far from an engineer, yet I try to help out others when I see a spot where I can.. and that's the general code of conduct it seems. What's nicest is that there's a handful (you know who you are!) of AWESOME folks that are truly hardcore engineers that live and breathe hobby electronics and microcontrollers.. and they chime in (without being jerks about it) when there's a need.
I've never seen anything quite like Arduino, and I certainly hope it just keeps getting bigger and better!