One of the most useful software tools that you can keep within reach of your computer is something that tells you how much information you upload to, and download from, the internet over a specific time period. And, of course, how fast those transfers are taking place.
Those figures allow you to check that your internet connection is working correctly, that you're not in danger of reaching your ISP's monthly traffic limit, and that there aren't any trojans on your PC silently uploading the contents of your hard disk to some foreign hackers.