Why is AJAX so popular all of a sudden?

Well the technology has been around for some time. But now that bandwidth for many users has increased, and simplification in design has become popular, so has AJAX.

Any time I can use AJAX to simplify the user experience or save on building a page, I try to use it.

Ajax has been around for a long time but it cleans very well and is so cheap compared to other cleaners. Therefore the price has made it more popular

...but will COMET become as popular?

Somewhere recently I read or heard about AJAX--hadn't heard about it for a very long time! Perhaps what I read, or heard, made some impact on the product and its sales. Sorry I can't remember the source!

AJAX = Asynchronous Javascript And XML

its pretty…(and fast)

glial is correct, the technologies behind AJAX (JavaScript, CSS, XML, JSON, etc.) have been around for a long time. It seems that these techniques just needed a name (coined, as it was, by Jesse James Garrett) and someone brave enough and high profile enough (Google Maps) to blaze the path for the rest of us mortals. That was the first app I remember seeing that really took advantage of AJAX in a smart way. The first time I used it, I knew the game had changed.

Used smartly, AJAX can make a web application much more responsive by making web pages interactive while sending much smaller payloads back and forth. Used dumbly, it can break a lot of aspects of the user experience.