No, they're not as minimized as they could be, but it gets to the point where you have to decide just how much mobility you're willing to sacrifice for a little extra protection here and there. The IBA is definitely more restrictive than an LBE, but it's not that bad, and, given the tremendous amount of protection afforded because of it, we're more than willing to make the trade-off. Now, there's also a lot of attachments for the IBA (throat protector, shoulder pads, groin pad, etc.) that add a little extra protection, but it starts to affect your mobility. Now, mobility on foot is not nearly as big a need for us now in Iraq as it was in, say, Vietnam, but there gets to be a point where you say, "No more armor. Let me be able to move, and I'll take my chances." Part of the Future Combat System is nanotech armor that wears like clothing but immediately solidifies when hit by a high speed object. That technology does exist now (although I think it's limited only to metal objects). Once that becomes fully viable, we can have entire suits made of it with little effect on mobility.
It's all just part of a trade-off. Me, personally? I'd prefer to be able to skip a full Kevlar suit of armor so I can still perform my job.