I have 2 desktops, 1 laptop, and one desktop used as a FTP server. All run 24/7. The one I am on now, I built 5 years ago, and except for a coupla moves & storms, it has been on all the time.
Laptop has been on 24/7 for about 95% of its 3 years in use, except trips when we use it in the car for a DVD player. Then it gets shut off when not in use.
Dell XPS 800 FTP server has been on straight for over a year now, don't even turn it off for storms. If it blows, I quit serving files.