Simon

Here is my code that I used it for client, it will generate 3X4 grid.
Shortcodes:

[catlist id=3 catlink=yes category_count=yes numberposts=12 thumbnail=yes thumbnail_size=150,150 title_limit=25 pagination=yes instance=1]
[catlist id=5 catlink=yes category_count=yes numberposts=12 thumbnail=yes thumbnail_size=150,150 title_limit=25 pagination=yes instance=2]
[catlist id=6 catlink=yes category_count=yes numberposts=12 thumbnail=yes thumbnail_size=150,150 title_limit=25 pagination=yes instance=3]

CSS:

.lcp_catlist {
	margin-left: auto;
	margin-right: auto;
}

.lcp_catlist li {
	width: 33%; /*this is comment if you wish the grid to be 3 in a row put 33%, if 4 then 25% if 2 in a row then 50%*/
	text-align: center;
	min-height: 150px;
	display: inline-block;
	vertical-align: top;
	margin: 0;
}

.lcp_catlist li:after {
	content: '.';
	height: 0;
	visibility: hidden;
	display: block;
	clear: both;
}