They are beautiful pieces of engineering too. Thomson seat posts are ovalized on the inside in the fore/aft direction. It intuitively makes sense, but if you do the actual math with moment of inertias about the centroid of the beam, it proves to be the optimal case. It makes it stronger in the direction when it bends from your weight, and lighter by removing material from where you don't need it, on the sides (because you don't need to worry as much about flexing side to side). I actually brought in my seatpost to show some of the students in the Mechanics of Materials class I'm TA'ing right now.

If an aluminum seatpost is NOT ovalized then it isn't optimized. There are a bunch of qualifying statements to that, but just let me say that the ovalization is smart hahhahah.