Lorel - 9:44 pm on Jul 8, 2010 (gmt 0)
I redesigned my 100 pg site a couple months ago changing the logo and color scheme and switching from a decade old Table format into CSS and my rank has remained steady for a multitude of keywords. I didn't move the menu however (which is horizontal across the top of the page) and I kept the same content and nav links. My traffic has gone down slowly but I believe this is seasonal as I get a lot of student traffic during the school year.
I also redesign several other websites per year and sometimes make drastic changes like rewriting file names (along with redirection in htaccess), changing titles and content, moving to another host, etc. and have never seen a drastic drop like was described in this thread, although it may take a couple months for the improvement in rank to show up in Google.