UseCase:
It was all fine before 2-3 years when people had just one machine, life was simple.. Browser was able to remember browsing history, login information locally on that machine. (Though, formatting machine and browsing on a newly setup browser was a pain..)
But now, life is not so easy.. Having three machines at work, one roaming laptop and home desktop.. almost everybody is surrounded by various machines, but the individual is still same. At the same time, Web 2.0 wave has increased usage of internet/browser exponentially. Now, I dont want to waste time remembering the URLs.. even sometimes I dont look at the address-bar in browser (I just want to focus on the content.. Hyperlink technology is simply great!!) so, I am not sure which websites I am surfing.
Now, just taking an example of yesterday, I read a blog article at one of my work machine and found it really interesting.. Came home, was thinking about the topic discussed on that page all the way while coming home.. Wanted to discuss one topic with the blogger, I had to go to search engine and search for particular keywords which led me to the article after 10 minutes of digging (during that process, I got to read few other important thing, but thats whole together a different story..) I did not find this way good and started thinking of way to solve this problem.
I think, what could be done is storing the "individual"s browsing history (which may include URL history, Cookies, Saved Passwords, Bookmarks, Open Tabs) all on the cloud. [[Being with Microsoft, I am thinking of IE implementing this feature first (I want my company to be the best.. 
)]]
Imagination:
Imagine having a service integrated with Windows Live which is built-in with IE, where in you enable the 'Live Web-History' option and provide live-id credentials after which all the history data gets saved in your windows live account. IE would have a built-in feature of keeping all the browsers in sync (having Microsoft released, 'Sync Framework CTP', and much efforts given behind 'FeedSync' at MS, this should be comparatively easy task..). So, going back to the use-case if I had browsed some page at some machine and wish to open it on another (assuming both are configured to use same account for saving data), it would be there in history. Having IE's address-bar a 'suggest' feature with full-text search would even add five-stars to the user experience (yet another user-demand, huh..).
I continued thinking on this about how to add value to this feature and got many ideas.. some of which are as follows..
- Search feature for browsing history
This would be really awesome! If one could go and search for entire articles content which he had visited during last X months, it would be like searching brain for knowledge acquired by browsing.
(it reminds me of somebody making a joke at Google, that in 2020, GOOG will enable users to search for something in their mind!!! LOL..) - Personalized browsing newsletter
One can have machines mine the data of individual's browsing history and learn what are particular's interests and prepare a weekly/monthly package with 'Recommendations' (RSS feeds can be of huge help implementing this thought into reality)
Imagine, I had visited some website reading some article and really liked it.. After some time, personalized browsing newsletter tells me that there is a new article on that website which 'I might like'... - Personalized Advertisements
If a machine can recognize patterns in one's browsing history personalized advertisements can be delivered all over the web which may give more realistic results for both ad-serving company and an individual (imagine if you are a student who has been searching for job from last few days, while reading a blog post, you see an advertisement with vacancy in a company.. Wouldn't that be COOL !!)
Having said that, I still remember Google having issues while serving contexual advertisements from people's emails. So, for this feature as well, Privacy can be a daunting question but having an option to enable this feature should answer that. - Auto-Login..
As I mentioned, if browsing history includes saved passwords and cookies, I never have to login again on all my different machines because IE should be able to auto-login me. I am very excited thinking about this.. There will be no more additions/updations in that excel sheet containing all passwords!!! (Though, CardSpace technology from Microsoft is supposed to solve this problem to some extent, but both features can go side-by-side, I guess..)
Current Status
While researching somewhat more on this topic (afterall, this was my 'Idea of the week-end' 
), I found currently few pro-active organizations have already implemented something similar to this..
- Google Web History
As always, Google has shown lead in this area as well (from where do they get all these ideas so early..!!! just kidding..)
They have their latest toolbar (still in beta) enabling users to make Google save the browsing history.. At least on IE, it works like charm right now.. So, I think I can get partial answer to my initial question using this.. Though, its not 'in-built' and I need to keep its Toolbar hanging all the times.. (Sometimes crashing my IE session..
Afterall, its beta) - Weave
The toolbar I just mentioned doesnt work on Firefox.. For Firefox 3.0 (which is still in beta) they have got a browser extension (which you need to install from mozilla lab.. again, not in-built solution) which lets you create an account for saving your browsing history (I think they just stores the URL that you visit)
But, sometimes it sucks, taking 100% of CPU.. I guess, while syncing machine's local history with that of web, it gets very busy that your DVD will not play for that time!!) - Google Browser Sync
Again, GOOG..
This has also got the same problem, it takes 100% CPU (that too on Normal priority thread is really a bad thing! They should implement it on low/idle priority thread, but anyways..), it can sync your browsers history.. Again, not in-built solution.. and it works only on Firefox browser.. - Windows Live Bookmarks (and many other online bookmarking services!!)
This is a good move, but doesn't help for the topic in question.
Having said all that, I know THE REVENUE, is nothing as compared to the efforts it require, but I remember attending a talk by a strategist, I liked it when he said, "Companies should not look at immediate revenue from an effort, its User experience that matters in Softwares, which earns profitability"
I think, this is the longest article in entire 'How would it be, if...' series. Everytime when I get an idea, I just avoid writing everything on blog, but this time I thought the other way!!
Feel free to post constructive comments, would be glad to discuss..
Stay tuned.. 