A recent post from the Opera Developer Community makes a case for why Ajax isn’t the great-and-wonderful thing it’s cracked up to be:
Striving for better things is not good enough, if in the process we lose some of our users completely. I think of progressive enhancement like a hierarchy of objectives: where accessibility is the highest, most important thing, followed by usability, followed by aesthetics. Ideally we want all three, but if achieving one of the lower levels means sacrificing one of the higher ones, then it’s simply not justifiable, in my mind.