When asked about Avatar 2/3, she said this:
"No. I heard that we might go next year so I'm really psyched," Saldana revealed about a potential 2012 start. "I'm keeping my bags packed," she admitted. "I would do anything for that man and for that project, so I'm waiting."
Well that's certainly interesting isn't it? We don't know much about the sequels, except that director James Cameron intends to shoot them back-to-back, a large portion of the second film will be set underwater and his team of nerds (not the CBM community) have to figure out how to do motion-capture underwater.
Anyway, Avatar 2 is planned to be released in December 2014 and Avatar 3 in December 2015!