I do stretches and stuff to increase flexability, especially the muscles pertaining to riding in an aero-position..

If you are training to do time trials and triathlons..Then I would say have your aero-bars on most of the time, as you will need to build up the muscles that are used in that pozish.

Also, a tri aero-position is different then a TT aero-position, do to different demands...(I dunno about you, but after a swim my arms aren't ready to be setup like Jan's in the Tour ITT's)