To those of you interested, have a newer version of the PSP duo stick and have some free space, you can download a demo for Peace Walker HERE.
Sadly, I have only one of those things (interest), and therefore cannot DL this thing, which makes me sad. 
However, let me use this opportunity to stress how excited I am for this game.  Anybody share my excitement? 
And for those who did DL it, how is it?  I'm sure we'd all like to know.

This demo has been out for a very long time. I thought it was fairly mediocre. The voice acting was patchy in places and I didn't care about the story. I found looking at a thirteen-year-old girl's panties through her clothes disturbing and ridiculous in light of the situation. The levels are linear and are essentially bottle necks where it's easy to get killed very quickly. I foresee myself having problems playing this game due to the loose controls on the PSP, but we'll see how it goes.
 
The Metal Gear series hasn't been good since 2003; that's barring the AC!D games which have been really, really good. The series just needs to be put to bed. It's boring, it's stagnant, it's irrelevant, and Hideo Kojima grows exponentially more annoying with every day that passes.

@ZanzibarBreeze:
Well, from a person's standpoint where MGS3 was their favorite, does there at least seem to be enough callback to that game/story to make it worthwhile? 
I wasn't necessarily expecting a lot from gameplay simply based on Portable Ops, but I'd be lying if I said I mainly played these games because of how "fun" they are.  To me, it's all about the spectacle.