MPE capable keyboards? Yeah...I have and use a CME XKey25, which has the "typewriter key-like" keys. I found that it took a bit of getting used-to regarding the action (or lack thereof), but after a month or two, I got very used to it. The nice thing about the CMEs as opposed to the McMillan controllers is that the CMEs retain a typical black and white keyboard with spacing, etc that we tend to deal with when using most any other MIDI keyboard. The only flaw I've seen is that every once in a while, there'll be a VSTi that needs some prodding to recognize the XKey...but that's minor, fixable in seconds.
The nicest thing, though, is that it fits very nicely in front of my Ableton-labelled computer keyboard. Score one for ergonomics!
As for the Continuum...y'know, I've been tempted once or twice to ask Lippold why it's so spendy, but I haven't. And if I really wanted one of those, though, I could probably dip over to his place (a whopping 20 minute walk from here) and pick it up firsthand...but you'll note that I haven't done either. It's still too academic-composition-oriented for me to risk dropping several thou on an experiment in controllers.