everything...voltages anyway. i still haven't gotten that intricate with it but it appears all voltages from vDIMM to vCORE to vPLL and so on are adjustable as well as FSB. and yes, completely on the fly...in Windows, during a benchmark, anytime. what i also just found was that when you change something through TweakIt on the fly, it does adjust it in the BIOS after you reboot as well. so basically, i believe you are actually changing the BIOS on the fly and the system registers it, even if your already in windows. it is completely hardware based though, no software involved.
and fire away with the questions, that's what this thread is for. i will be checking in regularily throughout the day to answer them all