Watching Damon and Carlton's panel at Comic-Con on YouTube, these are the items that stood out to me. Obviously they are spoilery, so if you don't like that sort of thing, don't read it:
* Season 6 will feature some characters we haven't seen since Season 1
* Faraday and Juliet will appear in Season 6
* Season 6 will not be pure flashbacks, flashforwards, or time travel--it will be something different
* In faux commercials, Hurley has won the lottery and owns Mr. Cluck's, introducing an Australian Outback chicken dinner after having a dream. Oceanic Airlines has cute flight attendants touting its perfect safety record.
* We will see Alpert's backstory
* We will learn about the DHARMA supply drops (as in 2x17, Lockdown)
* But there will not be a whole lot about DHARMA--they feel it was sufficiently addressed in Season 5
