Linux only: It's still a work in progress, but GNOME Activity Journal already offers a nice at-a-glance look at your file work over the last few days, offering usage charts, image previews and quick file access.
At the moment, GNOME Activity Journal can't do much more than present a nicer face for your system logs, and show what local files you opened, modified or saved. It shows the order in which you worked on your files, lets you "pin" certain needed files to that day, and, well, that's about it for now. Still, that's a lot more helpful than digging blindly through your recent documents list, and way easier than running regular expression searches on your system text logs.
GNOME Activity Journal is a free download for Linux systems. If you need help installing it in Ubuntu, the Web Upd8 blog has a handy little how-to on that.