Dub T asked in another thread why a front disc brake, and I thought it deserved its own topic.
Running disc brakes front and back seems to be somewhat of a trend now.
Bill Mc Cready of Santana is adimantly oppossed to using two disc brakes front and back. his rationale is that disc brakes can fade to the point of run out; if you have discs front and back, and overheat them to that point you are potentially left brakeless.
You've also got an issue with heat from a front disc being transferred to a carbon fork at high enough heat to damage the fork.
His preferred setup is rear disc and rim front. His recommended method for using that setup on long descents is to use the disc to control speed as necessary (supplementing with the front caliper if needed to slow sharply). When the disc begins to fade, use the front rim brake to stop, and let the disc cool off.
His explanation makes some sense.
Of course my personal bias is two rim brakes, no disc, other than for loaded touring, so I'm already biased against discs front or back.