I spent three hours yesterday and one today at a client site. Three quarters of that time was spent removing adware from two machines. One user's machine was so bad that it was pretty much unusable; I spent over two hours on that machine alone. The adware that had installed itself was downloading additional malware every twelve hours, was removing the autoexec.nt file, and deleting random fonts. My two tools found 316 and 72 malware infections.
Because I like you, here's some free advice.
Spybot Search & Destroy
Install both of these tools and use them weekly or so. Ask them to update their own files before you run them, and let them delete what they want. Your system will run much faster, and your surfing experience will be much nicer.
I took the picture with my new phone, FWIW. It's a Treo 600. It does just about everything you can imagine (I paid way less than the web site suggests, rabidkitten). Unfortunately, it doesn't work as a phone or internet node where I live; no GSM or GPRS coverage up here.