The shadows on his boxes appear to be a combination of images and CSS. The relevant code from his CSS file is:
.comment, .trackback, .pingback { position:relative;margin-bottom: 30px;padding:15px;border:4px solid #eee;background: #f8f8f8;
border-color: #ddd #ddd #ccc;
border-radius: 3px;-border-radius: 3px;-webkit-border-radius: 3px; -moz-border-radius: 3px;
border-style: solid;
border-width: 1px;
box-shadow: 0 1px 0 rgba(255, 255, 255, 0.3) inset, 0 0 2px rgba(255, 255, 255, 0.3) inset, 0 0 10px rgba(0, 0, 0, 0.1) inset, 0 1px 2px rgba(0, 0, 0, 0.1) !important;
-box-shadow: 0 1px 0 rgba(255, 255, 255, 0.3) inset, 0 0 2px rgba(255, 255, 255, 0.3) inset, 0 0 10px rgba(0, 0, 0, 0.1) inset, 0 1px 2px rgba(0, 0, 0, 0.1) !important;
-webkit-box-shadow: 0 1px 0 rgba(255, 255, 255, 0.3) inset, 0 0 2px rgba(255, 255, 255, 0.3) inset, 0 0 10px rgba(0, 0, 0, 0.1) inset, 0 1px 2px rgba(0, 0, 0, 0.1) !important;
-moz-box-shadow: 0 1px 0 rgba(255, 255, 255, 0.3) inset, 0 0 2px rgba(255, 255, 255, 0.3) inset, 0 0 10px rgba(0, 0, 0, 0.1) inset, 0 1px 2px rgba(0, 0, 0, 0.1) !important;
}
.comment:after, .trackback:after, .pingback:after {
bottom: -35px;
content: url("../images/shadow-after.png") !important;
position: absolute;
right: 0;
z-index: 1;
}
.comment:before, .trackback:before, .pingback:before {
bottom: -35px;
content: url("../images/shadow-before.png") !important;
position: absolute;
left: 0;
z-index: 1;
}
The "center glow" effect is actually the space between the left and right ("before" and "after") shadow PNGs. As far as I know, there's no way to apply non-uniform shadows in straight CSS.