I made a screenlet that shows your system’s uptime a while back, and posted it on my little-known site, http://nucco.org/?q=node/3 .
So, if you’re looking for a screenlet (Linux users) that only displays your uptime, I believe you will find this useful.
| Random quote: The History of every major Galactic Civilization tends to pass through three distinct and recognizable phases, those of Survival, Inquiry, and Sophistication, otherwise known as the How, Why, and Where phases. For instance, the first phase is characterized by the question "How can we eat?" the second by "Why do we eat?" and the third by "Where shall we have lunch?". — Hitchhiker’s Guide to the Galaxy