I have generally heard that the common consensus is to see how well LWW does and go from there. I'm not sure if that's dependable information, though? I haven't heard much about the studio's plans for producing more Narnia films. If they are being cautious, Nienna, I think it may be because the CoN are slightly more controversial (religiously speaking) than LotR. Also, LotR was immediately seen as a story with a huge audience range, from older kids to retirees. CoN, on the other hand, have always been seen as children's books.
Judging by the general obsession with fantasy, I think LWW will do well, which means that if that is the only encouragement needed to make more Narnia films, we should expect a few more at least. It's the idea that all seven of the books will be made into individual films that I tend to regard with a little skepticism, simply because I've never seen Hollywood stick with that big of a project and have it turn out well. That doesn't mean I wouldn't like to see all of the books made into movies. I'm just afraid to get my hopes too high.