Update Product List Column Layout
<catalog_category_default>
<reference name="product_list">
<action method="setColumnCount">
<count>4</count>
</action>
</reference>
</catalog_category_default>
<catalog_category_layered>
<reference name="product_list">
<action method="setColumnCount">
<count>4</count>
</action>
</reference>
</catalog_category_layered>
<catalogsearch_result_index>
<reference name="search_result_list">
<action method="setColumnCount">
<count>4</count>
</action>
</reference>
</catalogsearch_result_index>