What do you do when you have four levels of navigation on your website?
Some people told me to:
* reduce the number of levels to three and put them like that at
the top of the page (using tabs), others told me to
* put the top level (or even the two top levels) at the top of the
page (using tabs) and the other levels on the left hand side, and a
third group suggested to
* put the four levels on the left.
What are your suggestions and where can I find tests/reports on this?