Just had mine cleared at the dealer with the DRB II - most of the time they will do this for you at no charge.
The FSM confirms that the ONLY function of the Maint Req'd light is to remind the owner to replace the O2 sensor and other components and that it is only triggered by time... for older models ('91 is when they changed it I think) the timer was semi-mechanical, for newer ones it's all electronic and based on cycles of ignition timing, so there's no set way to know how many actual miles will fire it - I've heard that lots of high revving will cause it to fire sooner.
Also, it's not indicitave of the actual state of your O2 sensor at all, it's just a 'good idea' to replace it every 80k...I've got a nice O2 sensor tester that lets me check the condition of O2 sensors...neat tool. Replacing the sensor alone will not shut off the light.
...talk about generating repeat business for the dealers...