And with the heavy armor comes the support form it.. If the metal around it is thick enough, you don't need to add any support trusses inside of, say, the legs. The armor alone is enough to support the weight. Now, say, in another mech-ish case, the H.A.R. from One Must Fall, the whole thing is a complicated system of megnets repelling and attracting in very complicated fashions, and it is controlled by a computer that a human psyche can literally 'jack into' and your body is left behind, and your mind controls the whole HAR like it was your own body. You can easily 'jack out' of it easily, and your back to your own human body. This has almost limitless applications. If you make an HAR small as a human, a handicapped person can jack in and leave their human body behind. (Like Cossette, if you've played One Must Fall) One in-game application of the HAR is deep space mining on moons like Ganymede, and another thing they do in the example of teh Chronos, it has a system with enough power to modify the flow of time itself, and it can cause an area-wide freeze to gain precious extra seconds in rescue missions. They don't use the Chronos functions elsewhere, since it's an area-effect thing, and they can't move the system near as effectively on a ship, so they stuck it inside of a 90-story mech.
I know that was a huge swarm of nerd-ism, but another thing I see is the jumpjets in mechs. Gundams can do it, because they're mainly in space. A Mech, however, looks to be MUCH heavier than a Gundam, so it would take incredulous amounts of thrust to make it air-born. I guess that's why the Mechwarrior games occur in 3052 (or something like that) but from what we have now, it's not possible.
And I think what the biggest obstacle in mech technology is the balance. A human can lift a foot and he can bend his body to maintain his balance, and thus not fall over. A Mech, however, has no such luxury and would fall on it's side everytime a foot was raised. They would have to make it so the mech wouldn't topple over everytime it stepped. How that would be fixed is my dunno.
