The Golden Boy 

I would guess tires or wheels.

I have a Trek 400 Elance- it's a beautiful bike, I think it's the prettiest bike I own. For whatever reason, riding it was a neutral experience. I didn't dislike it, but I didn't like it. I changed wheels (actually went from 700c x32 to 27 x 1 1/8) and I found I really liked the ride much better. Whether it was the better hubs, a larger wheel, more or less air volume, different freewheel... I don't know. It was a pronounced difference in the way the bike rode.