I'm using Timesnapper and it's great. Not only it keeps screenshots for everything, but you can also filter by application while searching for an old website you saw or data that you forgot to save. It needs a lot of storage though. In 50GB you can keep 2-3 months of screenshots.
* Karm on KDE/Linux (tracking by virtual desktop, one for each project)
* Manic Time Tracker on Windows (very much like this but with a full GUI. Only works on Windows though)
* For emergencies on Windows there is also Timesnapper which in facts documents in screenshots what happened (in case you have to "prove" it .)
this utility seems like a real improvement on the current situation though. Thanks in advance!