im quite sure i read an article by jacob nielsen that said that right navigation gets seen slightly more (eyetrack confirms this) but that its use should perhaps be discouraged, since users dont expect it to be there.
i guess this is a bit OT, but can anyone advise that ads should go right and the nav left?
Believe it or not, Wichita State University actually has a "Software Usability Research Lab" that tests this kind of thing. In one study they found that users' expectations were to find internal site links on the left and external links and/or advertising links on the right. They weren't saying these were the best arrangements, just the ones that people expected. The result of that research seems to fit well with what stef25 said above. (BTW, they're very big on breadcrumb navigation.)