ProTour said:
Most pros run it level or slightly tilted up in the front, and for good reason. If it's tilted down in the front, it makes it difficult to use your pulling muscles(hamstrings) without sliding off the front constantly.
While Alberto Contador was boggling everyone by winning a TT in the TdF over Fabian Cancellara, I was noticing that he kept on munching his saddle - sliding forward with each stroke until he had to shove his **** back.
A slight upward adjustment of the nose would have equilibrated his position and stopped the extra effort of reseating himself, giving him back the energy he needed...to win by an even bigger margin...
That said, if he'd lost that TT, and for want of a TT lost the Tour, you can bet one of Astana's wrenches would have spent the rest of his summer adjusting the saddles on every bicycle in Kazakhstan.
So the moral is, be kind to your mechanics: learn to ride so fast it doesn't matter how your bike is put together.