There is a lot of good freeware out there, but you do have to be careful about what you use, a lot of it brings more harm to your computer that it does good, as far as Spybot, I have used the program on a couple of pcs that I have worked on and I find it to be pretty good and clean, maybe someone else can give their opinion.
Hope this helps.
It all depends on the software. There is some great freeware out there like Spybot and AdAware. However there is also some very bad freeware out there like Adware Alarm.