Update: 1st December Just had partial confirmation that this is true and I'll be making a post in the Spoilers section shortly.
Thanks to Kokin for the following, which I'm leaving in Rumours until we get some verification.
I work at a movie theater, and I happened to see the new promo tonight. First off, I had a major LOST geek moment when I saw the footage (wasn't expecting it). The promo is pretty short (details that the plane went down in 2004 and that rescue would be in 2008..or will it?). There are a lot of very quick cuts/dialogue from last season and season 4 footage. Everything happened so fast, but I do recall seeing the following...
-Jack firing a gun in the dark
-a cow/bull
-Locke claiming that the people arriving aren't here for them but something else
-a nonhuman skull with a knife in it
-blood dripping down and Kate looking up (at something/someone dead?)
-AND...what appeared to be Charlie. And what's even odder is that he had a devilish grin and what looked like short hair.
Overall, a very exciting promo (hell, ANYTHING new is great).