I've been using Spybot for several years now. I remember when their bot-checks hit 100,000. It's now over 539,000. I wouldn't be surprised if it hit one billion next year. The interesting thing is that it seems never to be finding anything. How many of these "bot checks" are for old and outdated malware which has since been neutralized? I would think there would be a way to speed the checking up. Here's all what I seem to have, and it's frequently nothing but this. It always says "Congratulations. No immediate threats were found." IE cookies. I never use IE, except for an occasional time when I have to use IE Tab in Firefox. Common dialogs, whatever the hell those are. History. Another weird IE thingy. Again, I never use IE. Several .log files.
I stopped using Spybot. I use Lavasoft's AdAware, and I hardly ever get anything pesky. I'm running Kaspersky Internet Security. I love the Russians. If anything shows up, they send this guy out.
I've used both Spybot and AdAware. Currently, I'm running the freeware versions of SuperAntiSpyware and MalwareByte's Anti-Malware. For anti-virus, I use Avast. No Russian backup, though. Maybe I should spend some $$ for the added muscle.
Right now, I have CCleaner, Avira AntiVir, and Spybot. It just amazes me that the Spybot list keeps on growing. If a patch exists for malware, and the malware in question hasn't made headlines in several years, then why check for it? Gotta check for that Melissa worm! (Wasn't there one called Michaelango a long, long time ago?)
I really like CCleaner - use the general cleaner feature daily. It was amazing (not really) how many errors the Registry Cleaner found after I installed Vista SP2. My guess it that you may be protected, but maybe not everyone else is. Although you may be patched and immune to an older trojan or other malware, you could still infect another's system if you inadvertently sent it on. So, Spybot still checks for the malware and neutralizes it. Though I'll admit that this is merely a guess.
I keep all my anti-crapware updated and I do run it from time to time. I also don't use torrents, or any p2p software at all. That reminds me, I should probably run it again, since I just installed Office 2007 and several updates. The first time running CCleaner is interesting. I KNEW there were a lot of dead registry entries, but to see them in a list was shocking. (And yes, the uninstall programs should actually, oh UNINSTALL their stuff. Argh.)