Atrios discusses why and how he became one of them radicals. For Atrios the pivotal moment was seeing how the media skewed its reporting on the inauguration. Well worth reading.
The inauguration was also a radicalizing moment for me... however, my take on it was obviously different than Atrios's. I assumed that the whole system was corrupt--that the media was working hand in hand with the republican party to create an overlord paradise.
The relatively swift passage of tax cuts for the wealthy, the slashing of the estate tax, and the imposition of harsh 'bankruptcy reforms' only cemented the notion I had that Clinton was merely a band-aid in the face of forces hellbent on the destruction of the middle class and the possibility of upward mobility.
For some reason, my cynicism remains quite intact to this day.