Why don't you take another approach?
If you have the need that users can view the same content over again, then it sounds like that is a business requirement for your application, and so you should be building it into your application.
Structure the URL so that when the same user (assuming you have sessions and the application shows different things to different users) visits the same URL, they always see same thing. They can then bookmark the URL locally, or you can even have an application feature that saves it in a user profile.
Part of this would mean making "clean urls", eg, site.com/view/whatever-information-needed-here.
If you are doing time-based data, where it changes as it gets older, there are probably a couple possible approaches.
- If your data is not changing on a regular basis, then you could make the "current" page always, eg, site.com/view/2008-10-20 (add hour/minute/second as appropriate).
- If it is refreshing, and/or updating more regularly, have the "current" page as site.com/view .. but allow specifying the exact time afterwards. In this case, you'd have to have a "link to this page" type function, which would link to the permanent URL with the full date/time. Look to google maps for inspiration here-- if you scroll across a map, you can always click "link to here" and it will provide a link that includes the GPS coordinates, objects on the map, etc. In that case it's not a very friendly url but it does work quite well. :)