For 2006, the Arduino was novel - a package that allowed one to access the power of a microcontroller via a serial port and software IDE. By 2009/2010 it was the gold standard in building smart electronics easily by vast numbers of Makers. Due to the law of ubiquity (the same law followed by the PC), Arduino will be around for a rather long time.
But are we heading into the Autumn of the Arduino lifecycle? The pressure is two fold:
1) Variety - the number of microcontroller boards now on the market is high with more every week. From smaller Atmel based units on Kickstarter to 32 bit devices with power a significant fraction of traditional computers. A large spectrum, including large numbers of clone devices. And the 2012 elephant in the room, the Raspberry Pi.
2) Price/Value - the official Arduino Uno devices are $30. The Ethernet and WiFi shields are higher than the controller they attach to. In today's market, the prices are too high in comparison to the variety of boards above.
Bonus point - in today's project market, smaller is better. The official Arduinos have remained the same size even as component counts have decreased. Ostensibly this is to remain compatible with add-on shields. But the Arduino project has broken this compatibility with the Leonardo - a contradiction. The component count is down but the price is still about $22 with few designs being touted on Marker forums.
With many Open Source efforts, the market leader stays ahead via innovation. Three products were announced nearly a year ago - the Leonardo and the official WiFi shield took months to appear, with the Leonardo's shield issues and the WiFi Shield using a huge controller chip, one more powerful than the processor it connects to. The final product, the Due is long overdue. The software to support the leap in power is quite complex to be sure but the silence is deafening.
So time marches on. The Maker community is adopting new technology and increasingly that is not from Italy. The tiniest boards are usually on Kickstarter, the mid-range belongs to Chinese clones, and the high end is is in a fight dominated by the Raspberry Pi.
Don't get me wrong, I am still a big Arduino fan and I wish them well as their innovation is really kick-ass. The market needs leaders to drive the pack - they do that to a T.
I paid $5 more for my Raspberry Pi - I'm off to program it for my latest project - for the extra cost I have 32 bits, video + sound, and Ethernet (but sadly fewer GPIO without add-ons) - and an exponentially growing Maker crowd to consult with on cool designs (I'll talk about the Pi soon). Arduino, where are you my old friend?