Teensy boards are great addition to Arduino family. In v2.0 they used USB AVR processors that made them smaller, more USB friendly. And for sure Arduino IDE add-on to enjoy simplicity of development. Paul Stoffregen has introduced Teensy 3.0 which was in development for about a year. This a major change in Teensy line because it uses ARM Cortex-M4 32-bit microcontroller.
Its main goal was to introduce ARM in to Arduino world without rise in cost, but rather giving greater performance and other ARM benefits. ARM offers better Analog input resolution, DMA, I2S, IR modulator, RTC and other useful features you wont find in AVR based Arduino. Teensy 3.0 is compatible with Teensyduino so front end is still easy to use as always.