Not sure exactly why it happens, but I found your problem.
CODE
#search {
left:75%;
position:relative;
top:40%;
}
Something with the left positioning is causing the page to stretch. I replaced it with a float, and it works fine.
CODE
#search{
float:right;
position:relative;
top:40%;
}
There is still a gap, but that is caused by the white content box. The margin and width attributes are conflicting for some reason. You can research on why this might be possibly, but simply take out the width from this:
CODE
#wrapper #centeringwrapper {
background-color:#F2E9D7;
font-family:"Trebuchet MS",Helvetica,Arial;
height:100%;
margin:0 auto;
padding-top:10px;
width:80%; <-- Remove this and the whole page looks fine
}
With those two tweaks in Firebug the whole page looks like I imagine it should.