Wilburforce - 12:22 pm on Feb 28, 2013 (gmt 0)
When was it moved to #75?
From page 4 to page 46 on 7 February, and from page 46 to page 73 on 18 February.
Did you sit and wait or did you do some changes?
I didn't make any changes to main page content, but implemented a site-wide menu change (from css to js) on 14 Feb. My Home page - the one that dropped - was spidered on 18 Feb (so that might have made a difference), but another page that has remained at #1 for its key phrase throughout the period was spidered on 17 Feb with no effect.
The js is disallowed in robots.txt, so search engines now only see the breadcrumb menu.
I did this to address two concerns:
1. To clarify site hierarchy for search engines;
2. To reduce the number of internal links;
In general, Google has appeared to be relatively tolerant of menus (and it has made no difference to other engines), so I doubt that this accounts for the movements.