I run it occasionally to clean stuff out and I would reccomend it to others, especially if you are having random popup ads or your computer is behaving a little more strange lately.
Lots of the free software you download comes with extra programs that help the software author get a little money even though he is giving his software away. These install along with the main program and run in the background, usually collecting statistics on what sites you visit or popping up ads occasionally. These extra programs are labeled spyware because of their stealthy nature (if you are notified at all it is usually at the bottom of the legal agreement you ignored when you installed the software) and their tendancy to send information to companies about your web surfing habits.
Spybot will remove these, along with common advertising cookies and maybe a few other things. Some of this spyware tightly integrates with Windows networking components and removing it can cause problems, while I’ve never encountered a problem running Spybot or the like I know some have.
A related program is Ad Aware. While these products mostly overlap in their capabilities, it is best to run both to be complete.
Both Spybot and AdAware are updated regularaly, like your antivirus program. You’d do well to keep up to date with these as well.
For years the answer has been an emphatic NO to the above question. Microsoft was kind enough to make life difficult for anyone who wished to maintain a semblance of site compatibility across the various browsers they have released. If you upgraded your browser to the latest and greatest (or not so great, considering the still remaining rendering bugs and security issues), you couldn’t use the last version that the millions of unwashed masses were still using.
The workaround was to partition up your hard drive and install multiple copies of Windows, one for each version of IE you wished to run. Or you could shell out a few hundred dollars for virtualization software like VMWare or VirtualPC and configure those to run multiple installations of Windows, each with its respective version of IE.
Finally this is no longer necessary. Joe Maddalone of Insert Title Web Designs (among others) deduced that some relatively simple changes would allow assorted versions of IE to run alongside each other. Even better, Ryan Parman packaged up all the necessary files and made them availabe for download.