I apologise for the less than factual nature of this writeup, but the previous writeups in this node have, I'm sure, adequately explored that aspect of the difference between poetry and prose.
For me, the difference between poetry and prose is one, essentially, of movement. When I write a poem, a good poem, a piece that I can be proud of, it gives me much the same sensation I get when I am dancing. I suspect this has a lot to do with how I write poetry: I focus on the metaphor or metaphors at the heart of the piece. Metaphors are how I interact with, view and explain the world around me. After exploring a particularly vibrant metaphor- such as in a poem- I sit back and feel something akin to euphoria. Prose, on the other hand, is reminiscent of walking. It can be just as pleasurable as poetry, there's no doubt about that. Sometimes I'd rather take a long, languid walk along a mountain path than dance frenziedly in a nightclub. I also incorporate many aspects of my poetry into my prose- to expand upon the metaphor, sometimes when I'm walking I break out into dance, take a few samba steps along the road (and, yes, that's something I've been known to do, particularly in recent months). But it's still walking, and thousands of others are walking alongside me.
When I dance, I dance for myself and myself alone. When I walk, I am always conscious of others around me doing the exact same thing. When I write in prose, I am constantly aware of my eventual audience, and this effects how I write. In prose, I am often stilted and wary. When I write poetry, I write it for myself above all others. It flows more easily. I've never tripped and fallen while dancing, only while walking. I like to walk. I love to dance. If I could, I would dance all the time. If I could, I would express every thought in poetry rather than just thinking in poetry.
I suppose this sounds pretentious, or at the very least, fanciful. But this, for me, is the difference between poetry and prose, especially as a largely self-taught free verse poet.
On a less personal note, poetry and prose often seem to me to have very different aims. Prose offers an explanation; poetry, a sensation or emotion. When language fails us, when there are gaps in what we can express in prose, poetry floods in.
Or maybe I'm just lazy.