There are a number of possible explanations, but it would have helped to have given us more detailed information, such as did yahoo work before you upgraded to Snow Leopard and which browser you are using (Safari, Firefox, etc?) -- rather telling us that you are "appalled"
The folks who answer questions on this forum are just regular Mac users, not Apple employees. So "attitude" won't buy you much free help here.
Assuming you are using Safari as your web browser, I'd suggest using the "Safari" menu to "Reset cache ..."
Additionally, since this sounds like a name resolution or routing issue, I'd type in the full correct name of yahoo in the address bar of your browser -- namely www.yahoo.com -- and not yahoo or yahoo.com -- or use this link:
http://www.yahoo.com
If that doesn't work, try using the IP address of www.yahoo.com, namely:
http://209.131.36.158/
If none of this works, please report back with fuller information about what browsers you are using and whether yahoo worked before your upgrade to Snow Leopard.