TheMadScientist - 5:09 am on Mar 10, 2010 (gmt 0)
One change in recent weeks, or certainly one that I haven't noticed before, is where Page A ranked for Keyword X and Page B did not contain that word and never has. Page A had very old, stale content and was deleted. An external redirect was added such that requests for URL A are now redirected to URL B. Interestingly, URL B now ranks for Keyword X even though that word is nowhere on the page, nor in the anchor text of any link (internal or external) pointing at the page, nor has ever been on the page.
Is the result semantically correct?