While we were sleeping in, Thanksgiving in the US, the Raspberry Pi folks released a new Pi. The Pi Zero is only $5. This is an amazing board, with 32bits of CPU, 512K of RAM and all the ports people would like, GPIO, HDMI and USB. It supports micro-sd for mass storage.
While the Arduino eco-system is in great shape, is there a reason to stick with an 8 bit CPU for most projects? The Uno and other boards start at over $25. Sure, you can get the boards cheaper on eBay and other Chinese importers.
The Arduino boards are perfect for many projects. If there is a simple input and output situation the Arduino is perfect for these situations. My garage door project is an example. The Bluetooth input, and the relay output makes the Arduino the simple interface.
There are other boards similar to the Rasberry Pi. The C.H.I.P is a $9 computer that has all the same IO as the Raspberry PI, but also has WiFi and Bluetooth built in. The C.H.I.P is still pre-order, but should be available soon.
The big deal with the 32bit processors like the Raspberry PI is it runs Linux (or Windows). That means development can happen on the board or cross compiled (more than likely cross compiled). It also means there are many debug tools available from GDB and tcpdump to a ssh console. The 32bit processors run quicker so other inputs (IE video) are more capable.
I've been planning on putting a 32bit board (waiting for my C.H.I.P) on my robot all fall. The robot will have an Arduino on it for sensor monitoring and motor control. The goal is the two processors will talk to each other and allow the 32bit processor handle thing at a high level, where the Arduino will be doing all the low level work.The 32bit chip can also run R.O.S.
There is a place for 8 bit processors, but more and more it is easy to pass them by.