There are many reasons to switch to Open Source. Here are a few:
1. Save Money for Yourself - Perhaps a better reason than any other.
2. Memory - A lot of programs are cluttered and drain your RAM. Most Open Source programs are as streamlined as possible, allowing you to multitask with other programs, like Half-Life.
3. One Time Cost - You won't be asked to pay over and over. Once you have the program, it's functionality continues at full-force in perpretuity.
4. Updates - Updates and Upgrades commonly are done for Free, and are offered automatically with an internet connection. This allows for a progressivly better experience with your programs as time goes by.
5. Sharing - Copying and Sharing Open Source software is not only allowed, it is encouraged, as the goal isn't to constantly squeeze money, but to reach as many people as possible who can help improve the product.
6. Bill Gates - He's rich enough, isn't he? Why give him any more of your money?
7. Security - Updating programs allow hole-closing and bug correction quickly and safely. Vulnerabilities are removed almost as soon as they are found.
8. Snobbery - Open Source means you get high class progams without having to become an Apple snob. No one is going to make you wear a stupid black turtleneck sweater, either.