I read some discussion (maybe find them back later) about that AJAX is replaced by AHAH and CTools in D7.
As I'm constructing a module rich site, it will take me at least a year to change to D7 when all those modules have been upgraded.
But I prefer to work with the new technology for D6, not the old one. Will AJAX be modernized for D6 to be fully AHAH?
Or would it be better to start a AHAH project and move all functionality of AJAX over to that project for D6, as well as for D7?