Bikes customised for time trialling are great. They are designed from head to toe with a focus on aerodynamics and comfort, making sure that you stay in your 'tuck' position as much as possible. However, there can be very good reasons for reconfiguring your regular road bike for occasional time trial use.
In my case, I have acquired a very nice road bike - the Ridley Noah 1303am - and it is so comfortable to ride that I have decided to try using it for time trialling. My main priority is to put tri-bars on and to get their position as low as is (comfortably and legally) possible. Here's what I've done:
The end result is a reasonably minimal frontal area, extremely comfortable and aerodynamic riding position, and easy viewing of my iPhone for tracking my progress. The only downside is that the gears aren't immediately accessible, but that should discourage me from excessive gear-changing anyway - the dreaded 'gear fiddling' that can set in on a tiring, long event.