Uptime is a measurement of how long your computer has been running without having been rebooted or turned off. Your uptime shouldn't be longer than about 16 hours, maybe 18. You have to sleep sometime.
Unfortunately, many people never turn off their computers. Energy use is at an all-time high and is only increasing. While I'm not a dyed-in-the-wool environmentalist, I am opposed to needlessly wasting energy when doing so is utterly fruitless.
Some people need their computers on all the time, and there can be legitimate reasons for this. If you need to compile a large program overnight, go ahead. Rendering a huge 3D image? No problem. Need to encode a bunch of video files and want to run it overnight? Go for it.
However, most of us aren't doing these things, yet we leave the computer on. People have numerous reasons for this, but most don't really hold water. Here are some that I've heard, and my rebuttals:
You walk into your office, press the power button, and take off your coat. You say "good morning" to a few people, and by then your computer is up and ready for you. This is perfectly reasonable when the alternative is running the computer for the 16 hours a day you're not at work.
The same goes at home. Get home, hit the power button. Put your stuff down, go through the mail (you know, the envelopes, not email). By now your computer is ready and waiting for you.
It may surprise you to know that many consumer level hard drives are built to run for only 8-10 hours per day. If you run them 24 hours a day, the failure rate increases dramatically. Running the system all the time may be causing the failures you are trying to prevent!
You may find people elsewhere who say that always running a hard drive is somehow "better" for it. Unless those claims come from a person who runs a test lab for a large hard drive manufacturer, they are just repeating rumors.
Fans react in a similar fashion to hard drives, because in this situation, the main failure point in both is the motor.
The longer answer is this: If you are running a server at home, perhaps hosting your web site and email, you are probably doing so because you're interested in learning how to configure and administer those services. Those services are also probably important to you. Unfortunately, those two things are opposed to each other.
To be a good System Administrator, you need to know that you don't do "learning stuff" on a production server, and vice-versa. If you want to learn how to do something, that's great. There are plenty of books and web sites explaining how to set things up. Use an old computer or VMWare as a testbed. This way, if you mess something up or want to try something new, you can do it without effecting your critical email and web sites.
There are many hosting providers who offer hosting plans under $10/month. Linux, ssh, database, php, etc... You name it. Your broadband provider may already provide a similar service at no extra cost to you.
Ultimately, using a hosting service lets you focus on learning what you want to learn, and more importantly (in the context of this article), allows you to turn off your computer for much of the day.
The biggest problem at work is that a temporary, "just testing" service quickly becomes mission critical. Before you know it, every time you reboot your computer, half the company has to stop working until it's back up.
If you turn off your computer every day, everyone will get the message that this is a "just testing" service, and use it accordingly. When enough people complain that your computer is down all night, management will take notice, and you'll get a promotion, a raise, and a parade celebrating how brilliant you are for creating that service. You'll also probably get a production class server to run it on.
...and you'll be saving the planet by not wasting more energy.
Seriously though, the concept of distributed computing is interesting and was worthwhile a few years ago. Back then, processors always ran at full speed, so there were many unused clock cycles going to waste. These projects sprang up to harness those wasted cycles.
Today, however, almost every processor adjusts its speed based on the needs of the computer at the time. When your computer is idle, CPU speed is reduced and the power usage drops accordingly. Software programs like this cause the CPU speed to increase, and along with it the power usage.
If you must participate in a project like this, please join one that will actually have some tangible results for humanity, like one of the projects trying to cure cancer or AIDS.
Anything you might gain from trying to avoid the startup spike are burned up within seconds of leaving the computer on longer than you need it.
I'm not advocating that you turn off your computer every time you leave your desk. Just once or twice a day. Turn it on when you first need it, and turn it off when you're done for the day. That's it. If your typical day consists of going to work, going home, and going to sleep, you'll be saving at least 16 hours of power usage on both your work and home computers.
You'll feel good about yourself because you're helping to protect the planet, and you'll find that it doesn't really hurt at all.