I also have this problem... for me, it appears anything hosted by Yahoo that requires logging in - this includes yahoo mail, groups, Delicious, Twitter, etc (these are apparently yahoo owned! I never knew..)
When I try to log in with Chrome, I get Error 324 (net::ERR_EMPTY_RESPONSE): Unknown error. Firefox and IE just fail to load and give me a blank page.
It works fine on my fiance's computer, which is on the same router, right next to mine.
I have tried clearing my internet cache, winsock fix, new mac address in router page, resetting router, etc... still no.