Bookmarks in AJAX sites

I am not working directly with Ajax bbut just curious about something.

In the Web 1.0 world, the back button was pretty easy. Simple fire the last URL get the last page. Now, in Web 2.0 (with lots of AJax) you can be on a page for 30 minutes and you hit the back button and instead of getting what you think is the last page, you leave the site completly.

My understandig is the Ajax solved this using # tags?

How?

Is it that things after that # tag never gets sent to the browser, so the state of the web page is kept on the client side?

So when you hit the back button. the text after the # tag changes to what it was, and this is just interpretated client side?

Enlighten me!

Cheers

https://developer.mozilla.org/en/DOM/Manipulating_the_browser_history
http://code.google.com/web/ajaxcrawling/docs/specification.html

Eric