I had the exact same problem as you do, so here's how I got through this on the latest Bootstrap version 2.3.1:
First you need to add a "no-space" class to the parent div with class "row" like this:
<div class="row-fluid no-space">
<div class="span3">...</div>
<div class="span3">...</div>
<div class="span3">...</div>
<div class="span3">...</div>
</div>
Then you modify your css according to number of elements you want in that row, like this:
.no-space [class*="span"]{
margin-left: 0 !important;
width: 25% !important; // This is for 4 elements ONLY in the row
}
The math for the width is:
100 / number of elements in the row = width.
In my case it was 4 elements so it's:
100 / 4 = 25%;
If it was 3 elements it would be:
100 / 3 = 33.3333333333%;
If you have multiple cases in a project with this issue, you might want to add a unique id or class to the css rule so it won't affect them all.
That's it. No need to redownload the bootstrap and to deal with source files
PS: This method works in responsive design as well ;)