I've been playing since 2.5b and have been lurking the PM threads since like May. I know that I am near the bottom of the spectrum in terms of skill and knowledge about this game, so I won't claim to really know what I'm talking about, but I thought I might as well share my personal speculation of what the current tier list might look like.
I organized it like a bell curve. I think it makes more sense that way.
S+ tier: Fox, Lucas
S- tier: Wolf, Meta Knight, Mario
A+ tier: Falco, Yoshi, Sheik, Wario
A- tier: Marth, Peach, Bowser, Diddy, Pit
B+ tier: Ivysaur, Mewtwo, Lucario, Snake, Ike, Sonic, Captain Falcon
B- tier: Jigglypuff, DK, Link, Ness, Ice Climbers(?), Zero Suit Samus
C+ tier: G&W, Kirby, Luigi, Samus, Charizard
C- tier: R.O.B, Zelda, Roy, Olimar(?)
D+ tier: Toon Link, Dedede, Pikachu
D- tier: Squirtle, Ganondorf
(I sort of guestimated on Icies and Olimar, since I don't feel confident in my understanding of those characters.)
Thoughts? What did I screw up the most?