1So as far as AJAX is concerned...
2
3Pressing back while using most web-apps that use AJAX to navigate specific parts of a page is a HUGE issue. I don't accept that 'having to disable the button means you're doing something wrong' and in fact developers in different facets have long run into this problem. Here's my solution:
4
5window.onload = function () {
6    if (typeof history.pushState === "function") {
7        history.pushState("jibberish", null, null);
8        window.onpopstate = function () {
9            history.pushState('newjibberish', null, null);
10            // Handle the back (or forward) buttons here
11            // Will NOT handle refresh, use onbeforeunload for this.
12        };
13    }
14    else {
15        var ignoreHashChange = true;
16        window.onhashchange = function () {
17            if (!ignoreHashChange) {
18                ignoreHashChange = true;
19                window.location.hash = Math.random();
20                // Detect and redirect change here
21                // Works in older FF and IE9
22                // * it does mess with your hash symbol (anchor?) pound sign
23                // delimiter on the end of the URL
24            }
25            else {
26                ignoreHashChange = false;   
27            }
28        };
29    }
30}
31As far as Ive been able to tell this works across chrome, firefox, haven't tested IE yet.