I will be working with them as soon as my breakout boards come in the mail.
Let me give you a rundown of these chips:
First off, they are I2C, as in you only need the power lines and then the SDA and SCL lines. That means that you can use this without it's own library, you can instead use the Wire library. Its own library would make it easier although through practicing with I2C, and reading the datasheet thoroughly, you can use them fairly easily. You can find videos and tutorials about I2C on youtube.
Secondly, the way that this chip can PWM so many leds with so few pins is because it drives charlieplexed arrays. They call it crossplexing, but its charlieplexing. You can see the diagram of how the leds to be driven are set up. One pin connects to a row of anodes and a column of cathodes, the next pin connects to the next row of anodes and the next column of cathodes, effectively making the array charlieplexed. You can read up on charlieplexing on wikipedia as well as at Grumpy_Mikes website.
Thirdly: These aren't cheap chips. You can get a sample from them for 3 of the chips although for purchasing them, they only take orders over 1000 pieces from their website. I believe one of the major distributors (Digi-key, mouser, jameco, futurlec, tayda electronics, not sure if its one of those or one I forgot) sells them piece by piece. Buying them one by one sets a price of about $6.00 each. Buy in bulk, and you can drive that down to about $1.99 a piece at 1000 pieces.
Do me a favor and reply to this so that it is in my replies and I remember to let you know how my experimentation goes.