No pussyfooting around, let's obliterate ads once and for all. First, go to the yoyo site
and copy the list of evil ads servers in the proper format. Hosts file format is good. Copy the whole thing (you don't need the comments at the top). Now, hang on to this for a minute. Now comes the tricky part. You have to open Text Edit as Root via Terminal. Here's the command: sudo /Applications/TextEdit.app/Contents/MacOS/TextEdit /etc/hosts
Again, this opens Text Edit as root user, so be careful. PLace your cursor at the end of the list in the hosts file, hit Return so you're on a new line, then Paste the list you copied from yoyo. Each entry should look something like:
As your are now a root user, be sure to save your changes to the Hosts file, Quit Text Edit, Quit Terminal, log out or restart. These ads won't even make it to your browser now, as the front door will be slammed in their face. Omniweb, Webkit, and others are much nicer to browse with.
If you find too much is being blocked, you can go back into Hosts the same way, and remove servers you don't want blocked.