So this is an article to note an oddity when I was working with a Yootheme template called "yoo_sync". Some clever scripts (both mootools and jquery) using the equalize method to make div layers the same height, and in this case, the same width. It isn't so much a miscalculation of 100% divided by 3 that leaves 1 pixel left over, more the fact that the scripts use that 1 pixel (ceiling rather than floor?).
We have a row on a website of three boxes made of div layers. When viewed normally on a 15" Laptop, all was good using Chrome and tolerable using MS Internet Explorer. If we maximized the Google Chrome browser, the row would split and there would be 2 boxes on the top row and the third would pop under these. As for MSIE, that was ok when maximized.
You could do loads of code hacks which is what I tested but all for nothing because you always end up needing to specify a third of the width.
Our template was 900 pixels in width. I tracked down some code that was simply calculating with 33% as the third of the page width.
Changing this to 990 pixels in width fixed the problem. I'm guessing this was because 990 divided by 33 leaves a remainder of zero but I'm not 100% sure this fixes the issue throughout other systems.