http://mvps.org/winhelp2002/hosts.htm
"What it does ... The Hosts file contains the mappings of IP addresses to host names. This file is loaded into memory at startup, then Windows checks the Hosts file before it queries any DNS servers, which enables it to override addresses in the DNS. This prevents access to the listed sites by redirecting any connection attempts back to the local machine. Another feature of the HOSTS file is it's ability to block other applications from connecting to the Internet, as long the the entry exists.
You can use a HOSTS file to block ads, banners, cookies, web bugs, and even most hijackers. This is accomplished by blocking the Server that supplies these little gems. Example - the following entry 127.0.0.1 ad.doubleclick.net blocks all files supplied by the DoubleClick Server to the web page you are viewing. This also prevents the server from tracking your movements.
Now includes most major parasites, hijackers and unwanted Search Engines!"
YES! I forgot about the hosts file trick! I've got a version that I downloaded as a text file, which lists most of the known IPs for spyware and ads. I haven't installed it, but I have it in case I get the whim to do so.