Ajax cons?

I read a tutorial on ajax and as I would assume the tutorial was very pro ajax. It didn't fail to mention anything short of great about ajax. I have a major problem with that -- if ajax is so great then why isn't everyone using it?

I'd like to know all the cons there are to know about ajax. Two things in particular are usability and seo. I'm wondering how many people actually browse the internet with javascript disabled. I'm not too concerned with users browsing from a phone or from an ancient computer as my website really doesn't target that demograph. But the biggest concern is really how it holds up in seo. I don't think a serch engine can spider an ajax web page, but the tutorial failed to mention if that was an issue or not (probably because if it isn't then there wouldn't be a reason to mention it).

Ajax seems conquerable, but doesn't seem like a walk in the park. So if there are good reasons not to use it then I probably wont. I would really appreciate any reasons you could give to use it, and not to use it.

Thank you for your time.

Cons

1. You have to call the server every time which can be extra wasted bandwidth especially if you are using Ajax just for the novelty of it.
2. It is not search engine friendly so search engines might not properly index your page.
3. It does not work with older browsers

Even with those cons I believe Ajax is more then just a fad and the reason why you do not see it as much is because it is only recently gaining popularity. Sites like google maps and mail both incorporate Ajax.

The usual alternative would be a full page reload, though, which would use more bandwidth.

There's quite a few drawbacks - there's a good list here.

Another one I'd add to that list is "security issues". I'm sure there's all sorts of fun security problems to take care of. For example - I'm betting that we'll see all sorts of AJAX callbacks to check user details etc, unless you're using SSL then this will be highly sniffable, as well as editable.

Oh - and I have issues with XML - it's overkill in most situations, JSON's much nicer.

Edit: just found a good article on AJAX security here.

I'd like to add a few alternatives to strict javascript and xml AJAX--flash based AJAX.

FJAX and Lazlo

Both add a little extra security in my opinion for making remote procedure calls by using Flash's security model as a front end. But as the both of SimonGreenhills' articles mention, design is a heavy factor for security in all AJAX-ian technologies.