Thanks for the replies.
I probably should've described my situation better. I'm offsetting the scrollbar of an overflown element so that it is well outside of the box. The problem is, a scrollbar is considered part of a box's flow. Of course, it is this way for obvious reasons: e.g. pushing all the content to the left slightly if a scrollbar needs to be placed on the right, thus making sure the scrollbar doesn't cover up any content.
That creates a problem for me, though. This means the content in my box will be offset differently based on the width of the scrollbar.
I'm really hesitant about doing this, as it is a main part of the layout. It looks great cross-browser, it even works in ie8. I'm just not sure if it will work cross-OS.
Now that my mind is more put to ease about scrollbar width, I'm worried about the default position of a scrollbar. Personally, I have never seen an operating system that positions scrollbars on the left of the window, but if there were one, it would absolutely destroy my layout.
Has anyone seen an OS interface with a scrollbar on the left? :)