We just got our first Adafruit Trinket Pro yesterday and have it all ready to test on the Hack-E-Bot. Unfortunately I have not had the time to program it yet, but this bot has a few other advanced mods from Adafruit as well.
By using the more advanced Trinket Pro, we can add more advanced sensors. The first that I will be trying out is the HMC5883L Triple-axis Magnetometer (Compass). This should allow the Hack-E-Bot to drive in straight lines and turn more precisely by moving in relation to a compass reading.
The other major mod for this bot is a rechargeable replacement for the 4AA battery box. I have used the PowerBoost 500 Basic, Mini LiPoly charger, and a 2200mAh Lithium Ion Cylindrical Battery so that the robot can be recharged rather than having to replace the batteries.
These will hopefully become part of the ever growing upgrade options that we come up with for Hack-E-Bot.