Specialized Transition Elite alloy frame (left), Transition Comp FACT carbon (right)
We've got Transition Elites, Comps, and Experts. The Expert is black and white and is equipped with Shimano Ultegra components. The Comp has SRAM Rival. They've got super stiff and super aero frames with internal cable routing and, seat posts that have two setback positions: standard or zero-offset.
For test rides and fitting the bike, we've got this:
The first thing I noticed test riding this bike was how easy it was to sustain high speeds. There is a noticeable difference, compared to, an Allez. Specialized claims that 70%-90% of a cyclists power goes towards overcoming aerodynamic drag, and that number increases with the square of your speed. In other words, it takes more than twice the effort to maintain 30mph than 20mph.

Transition Expert. FACT 7r frame, Ultegra all around. In the picture it's got the test ride/fit alloy seat post.
So how much faster is this bike than a road bike? Well, that depends on a lot of factors. I dug up a study that Specialized did in 2008 that concluded their Transition was about 10% faster than a Tarmac SL2 with the same power output from the rider in real world scenarios. That's a pretty big improvement!