Here is a useful and interesting journal paper on navigation comparisons for high traffic websites with main navigations on both the left and right hand sides.
The research questioned current leading Web design thought that the main navigation menu should be on the left hand side, and was conducted by James Kalbach and Tim Bosenick from Razorfish Germany.
The paper comments on the effects of navigation position on usability, efficiency, affordance and perception, learnability and some of the advantages and disadvantage of both. The hypothesis was that the left-hand navigation would perform significantly better and faster, instead, there was no significant difference in completion times between the two test conditions.
Here are other links to Usability papers by JoDI (Journal of Digital Information) – ISSN: 1368-7506