I can only speak from a US-centric point of view, as I was in the army from 2005-2011.
I honestly don't see power armor becoming a serious infantry weapon platform. Barring some totally incredible breakthroughs in materials science and energy production/storage systems, it will continue to be more cost effective and require fewer training man-hours to use mobile artillery and air-to-ground heavy strike weaponry for missions requiring the delivery of serious firepower.
Even assuming that all the technical hurdles were overcome and that practical power armor could be used in field conditions, the training aspect alone would keep the numbers of such units low. Common soldiers already have 15 tasks, 76 subtasks and four battle drills to be fully trained in. That's JUST in basic training, not including whatever they need to know for their military specialty. When I joined in 2005 it was 32 tasks, 207 subtasks and 12 battle drills. The trend is to simplify training as much as possible.
Artillery and helicopter crews have to split up operational tasks and responsibilities because the systems they operate are so complex. The Patriot anti-missile teams are even more compartmentalized and specialized. Basically with weaponized power armor we're talking about the equivalent of a tank or a helicopter in complexity, operated by a single soldier. You can only handle so much of a system that complex with automation, which of course can fail, and then what?
There's a limit to how much data a single mind can cope with, especially under stress. That fact implies that a similarly limited number of individuals will be able to adapt mentally and physically to running something like a powered suit, in the same way that a limited number of people can handle flying an F-16.
In the end, I suspect that we'll see much more emphasis on UGV and UAV technology, which has (in some instances anyway) already proven its worth and has at least the beginnings of a sound tactical and strategic doctrine in place.
I'd put money on seeing iterated variants on the Crusher, the Switchblade, and the Raven in the field, and the power armor strictly in the PR briefings, for the next few decades or so. They require significantly less training for operators, use present technology, don't expose the operator to hostiles, and fit nicely in the corners of the budget.
http://www.rec.ri.cmu.edu/projects/crusher/
http://defense-update.com/products/l/switchblade_31122010.html
http://www.af.mil/information/factsheets/factsheet.asp?id=10446