From the top of the postbits here:
HTML Code:
<!-- post #1524601 -->
<div id="edit1524601" style="padding:0px 0px 4px 0px">
<!-- this is not the last post shown on the page -->
They set the padding between posts to be 4px. That is from the postbit_wrapper and set by the $stylevar[cellpadding] variable. It looks like they may have elimated the spacer_open (and spacer_close) templates there. If you don't want to fine/delete them, then edit the spacing in there too.