A website without ajax is very rare now a days. Gmail gave us the exact feeling of online by lively giving information of mails, chats etc. Ajax is exploring world wide web through n! (n factorial) Dimentions. Many pages websites are minimized into a single page website and rest part gives to ajax to load. Browsers back button has less meaning while using fully ajaxed websites.
For example: http://www.campaignmanager.in
Search Engine optimization also facing another problem due to this ajax. The spider crawling among websites link points are “html links”. They crawl from one page to other through links. But in the case of ajax, if the next pages are the result of an ajax call, the spider cant proceed further crawling… For that purpose, the developer should concentrate on search engine crawling while the creation of fully ajaxed sites (if needed).
A Sample Source Code: