I've seen plenty of great AJAX apps, especially for the enterprise. The problem is NOT with the technology, it's with the programming.
Forrester obviously doesn't understand that. They don't find any good AJAX apps (one wonders where they're looking), so something MUST be wrong with AJAX. Their recommendation: explore other technologies, including Microsoft's.
Run, don't walk, the other way from "research" like this. Look on the bright side - you're not the poor sucker who had to pay for it.