If you're reading this blog entry I guess you're having problems with adding AJAX in your commerce_cart_add_to_cart_form.
So this blog post is a reminder for myself if I should ever again run into this problem.
What I wanted to do, was adding some AJAX functionality to the add to cart form (A product add to cart form in the shop) using HOOK_form_commerce_cart_add_to_cart_form_alter.
But it just did not want to work. No ajax calls were executed.
Finally I found out that a conflict with the dc_cart_ajax.module was the reason. Maybe a module weight conflict or something logical (I think that's the case).
I did not yet analyse the reason in deep and firstofall disabled the module - but hope this blog entry may preserve you from a very time consuming bug tracking...