I am a Senior Software Developer at Adobe Inc.
I was Research Director of UC Berkeley's Center for New Music and Audio Technologies (CNMAT)
I don't use the stock "official" Arduino boards for my work. The $18 teensy 2.0 is smaller than any of the stock Arduinos, has more A/D pins than any of them except the Mega, has more memory, more PWM pins, full speed USB serial support and has a more accurate crystal cock instead of a resonator. You can buy them from the designer ($18$16) or from Lady Ada ($20). Sketch loading and restart is much faster because of the high speed USB port.
The FTDI drivers aren't necessary with the Teensy and you can add the Teensyduino overlay to run your Arduino sketches.
The overlay has several high performance features the Arduino core group haven't got round to yet: the A/D is run in high speed mode and the serial port implementation is efficiently interrupt driven on input and output.
So what is the catch? Some hardware improvements I suggest: get the silkscreen right for Arduino nomenclature, move the led from an analog input to a digital pin and build it with the 3.3v regulator on board and a switch (like the seeeduino boards) ditto for the teensy++. I would pay the extra few dollars for this.
If I really have to use the original Arduino form factor (to leverage a useful shield) I use the seeeduino or olimexino. They are compatible, comparably priced and have some handy extra switches, power supply features and break out the 2 extra A/D pins often omitted on other boards.