Full text of the letter from Yahoo! to MS:
http://www.businessweek.com/bwdaily/dnflash/content/apr2008/...
"Moreover, Steve, you personally attended two of these meetings and could have advanced discussions in any way you saw fit. "
Microsoft has put forward their offer and is awaiting a response. It's not as though Yahoo has forgotten about it -- the next move is theirs to make.
Microsoft has basically said "Hey, guys. We made an offer that's more than a 60% premium over your share price. If you won't accept that (or even let us know what price you will accept) we'll take this right to your shareholders and do this the hostile way at a price that's lower than our current offer."
The ball's in Yahoo's court on this one.