On the Prevalence and Removal of Spyware?

oo7tushar asks: "There's a lot of spyware out there these days. As a Windows/Linux user I'm concerned about what spyware is installed on my machines and I'm very concerned about this issue when it comes to Windows. A few questions for the masses: What are the most common spying applications that are installed? How do I get rid of them without getting rid of the parent application? Have you encountered spyware on Linux?"