Let me be more specific. Round tube aluminum Treks using Easton or Alcoa tubing are generally nice, compliant rides.
When Trek changed to Alpha SL tubing with triangular section downtubes as in randyjawa's 2200 above, ride quality took a hit IMO.
Seemed as though Trek was appealing to a different (racing) crowd now. One that didn't mind harshness in the sake of speed and efficiency.
The Alpha SL frames struck me as stiff and jarring in comparison to their Easton or Alcoa brethren. That nice compliance was gone.