I've read a few articles recently about Googles newly launched AJAX driven Directory on Google China.

AJAX applications, as I understand them are created using Javascript which the search engines can't read.

Normally, this would be where everyone starts crying "No - Don't Do It!", however with Matt Cutts recently talking about how search results should be kept out of the Google SERPs, it can make sense that if the search results should be excluded, then it is easier to do this with a method that search engines can't/wont read than to go out of your way to exclude them. It creates pageless pages that the Search Engines can ignore.

AJAX also fits in perfectly with Google personalisation drive, as it allows interfaces to have greater levels of personalisation. There is chatter about how the uptake of AJAX is set to exponentially increase over the next 12 months.

Another one to keep an eye on I guess.