I think were really edging into the area where personal definitions are really the issue.
Does a "Magic Bean" really ever need to be explained. I would argue that as long as we have an idea of what it is in concept, that is enough.
If we go with the arguement that "magic" is the magic bean in Harry Potter, it's not like we need to know HOW it works, rather that it does.
The magic bean of Sixth Sense is most assuredly the fact that this kid can "See Dead People" but ... yeah it's been a while but do we really ever know why? I don't think so and that's fine.
I would argue that both Magic Beans & Mcguffins are by there nature better off unexplored.
We see vailidity to that when we get the god awe-full miteclorians (sp) in Phantom Menace, which is a blatant attempt to explain the magic bean of the Force.
(as a side note, I always rationalized that one as a causality issue, these Jedi had noticed that all the force users had a measurable amount of this micro-organism in proportion to their ability, but cause and effect were never linked, I always thought it made more sense that it just happened that there was this bitty thing that was really attracted to a property of the Force using persons physiology, or static cling, and they just gathered more around and inside them the more powerfull they were. So once again basic logic failed them, just like the thinking that "balance to the force" would mean good would win ... umm doesn't balance infer that you would be essentially stalemated with the opposition? and thats were you ended up ... so result)
Sorry got sidetracked.
Yeah so I think that we could really argue that the Island was the "magic bean" we partially tried to explain it over the season, leading largely to more questions (electromagnetism and energy pockets) and then again at the end with the cave of glowy light energy, but that resulted in the same kinds of issues as the Star Wars justification.
It just is, deal with it.
And while I personally was happy with the FlashSideways resolution of "purgatory" I can definitely see the argument that it's a second bean out of nowhere, preying on the previously established formats of flashing back and forward. I just find myself giving them this one.
And no, working on Lost in its final season isn't influencing my perspective much, I still came at pretty much each episode as puzzled as to what was going to happen as the general populace.
Well that was a nice long ranty first post.