Mydoom.M uses Google, Yahoo, Lycos and Altavista search engines to find email and domain addresses. As a side effect the infected computers can not access these sites.
This is not the first Mydoom that affects a particular web site. Previous Mydoom variants intentionally targeted SCO and Microsoft. We don't think Mydoom.M prevents access to Google, Yahoo, Lycos and Altavista intentionally - this looks like a side effect.