This one comes under the conflicted heading of “fairly nifty / kind of creepy.” IBM’s Research Labs have come up with a Firefox plugin called CoScripter Reusable History that records every single click and entry you make in the browser — and then lets you search, replay, and share that history, hence the “reusable.” This graphic (click to enlarge) will give you a quick sense of what’s on offer here. (There’s also a video and a further explanation here, that should clear up any confusion.)
I can see some uses for this — and, of course, some dangers for the foolish. (I should note right away that the app does not record passwords.) This might be a very useful tool for someone wanting to test and improve the usability of a website: okay, it won’t record the eye-movements of the test subject (thank goodness), but it will leave a very handy trail of clicks and starts. Too, the video shows the developer searching his browsing history for all of the instances in which he entered his name into a text box on a website; I can see that being useful under some circumstances. And, I suppose, the sharing aspect of this could make a decent way of showing someone how to accomplish a task on the web.