Ehh... I've done a lot of research on the free one's like Avast and AVG Free. They never do very well when it comes to actually detecting the virus, and when it does it never actually removes it sucessfully.
It's nice to see that Symantec is making improvements to make their software lightweight. They reduced the installation size by turning off Windows System Restore during the installation [ref:
http://www.eset.com/threat-center/blog/?p=153] That seems kinda shady to me, wouldn't you think?