The E-3 is built by old churces and German Leopard II tanks. It's as sturdy as anything out there (and I handle anything from 1Dmk3 to D3 on a sort of regular basis, so I should know what I'm talking about).
Truth be told, the weight and solidity of the E-3 did suprise me quite a lot the first time I handled it (I was using the E-400 on a daily basis).
Nowadays, though, I don't notice it. It's become very light, very small, and I don't think about the sturdyness.
Though, it's been covered with rain, it's been treathed the way most press photographers do treath their cameras (I shoot press), and it's taken the abuse with no problems at all.
When it comes to build, I don't even think stuff like the D3 or 1Dmk3 is better built. That is why the E-3 is as expensive as it is. It's just bullet proof.