I would just like to point out that the Teensy is "Arduino-like" versus "Arduino compatible". What I mean by compatible is that Arduino sketches can run unmodified. The Teensy does not have any Analog inputs and so is not compatible. The larger Teensy++ does have Analog inputs but is larger than the om328p. The Teensy bootloader is also closed source and not available to other people. This kinda defeats the object of the Arduino platform.
It is clear that Paul has spent a lot of effort on the Teensy to get the hardware and software correct and I applaud what he has done. One of my next projects is going to use the USB capable Atmel ATmega32U4 so I'm interested to see how the Teensy bootloader and downloader works.