See Windows - New Web Font Blurry - #32 by Chock
Also, I use Lucida Grande, Medium fonts, and add the following CSS then everything looks pretty much the same as before
.NB-theme-feed-font-whitney {
font-family: Verdana;
}
.NB-storytitles-title {
font-size: 13px;
line-height: 15px;
}
.NB-feed-story p {
font-size: 14px;
}