I've been doing some projects with this board testing it out. For under $8 the Trinket offers 8MHz (overclocking to 16 MHz is software possible on the 5V version). It has 8K of memory which is enough to do a lot of smaller projects. With it's 5 multi-purpose digital pins it's very versatile and an easy choice for inexpensive projects. The best resource for getting started with the board is of course on the Adafruit site: http://learn.adafruit.com/introducing-trinket/introduction.
However, I would not recommend this board as the first board to try for someone new to micro controllers. The programming process a bit tricky compared to other boards like the Arduino Mega, Uno, and Micro for example. Also, the board does not have Serial USB capability like other boards have so it's very difficult to debug on this board. For anything that is more complex, I have found myself prototyping with the Arduino Micro and then porting it to the Trinket.