Now that I finally have both an Arc and a Grid, I feel compelled to urge anyone who is interested in expanding their ability to control their sound production to get a Walk. Obviously, it's a bit overshadowed by the much greater sophistication of the two aforementioned instruments, but it's partly because of that that it's so fundamentally excellent.
In fact, I'll go further and say that any committed Monome user is morally obligated to get one--and save yourself the trouble and just buy one with the pedals, unless you have them already.
It's such a blindingly great way of expanding your input possibilities. Drummers, especially, will really get it.
I'm using it mostly in Momentary mode thus far, and haven't even touched the logic aspect, but seriously, it's the best $140 you'll spend on Monome.
Both feet working rhythmically while your hands are Arcing or Teleplexing or Gridding or whatever is just...sublime.