After some frustrating efforts we found a simple fix for a set of pages that would often not load at all, and were at the same time seeing bandwidth usage shoot through the roof for no obvious reason.
If you're linking to a page containing WordPress Post Tabs, the link must have a trailing slash. Otherwise it can cause an infinite loop of embedded loading pages within the tabbed area.
We didn't see this at first because our Firefox automatically adds trailing slashes, but Chrome and IE don't.
I hope this helps someone else out!