I have a good amount of experience with computers, and have been using Spy Sweeper with Antivirus for several years. It has been hassle-free which I appreciate. I recently upgraded to SecureAnywhere on my family's five PCs. We are active Internet users. Two are Windows 7, two are XP, and one is Vista. Installation was surprisingly quick and trouble-free. I like the fact that scanning is quick -- my new laptops with Energy Star features are asleep much of the time. I also like the small footprint -- as others have commented, I am not aware that the antivirus program is there.
I read Neil Rubenking's review in PC Magazine with great interest. He seems to be very knowledgeable, and to have a thorough test suite.
In the initial scan with the new product, one of my PCs found a malware infection that the older product had missed.
No antimalware program is perfect at blocking. Webroot has a support feature that I appreciate, and have used twice over the years. Their Professional Services staff will remotely access your computer and remove malware, if needed. The service is not inexpensive but they are very knowledgeable and responsive. I registered via the Webroot website, got an appointment the next day, and a difficult infestation was removed.