Spyware, in my opinion, is far worse than viruses/worms/Trojans
Yes.. besided the problems that the Spy/adware Parasites directly cause, ie system slowdowns, and internet/network connectivity issues, they appear to become a backdoor to the conventional malware. what is becoming common is the Kernel Hijack, and it seems to start with the adware trojans.

I would add one extra tool for selfdefence, an adblocking Hosts file..

cheers