crobb305 - 12:11 am on Mar 31, 2011 (gmt 0) [edited by: crobb305 at 12:14 am (utc) on Mar 31, 2011]
Add to your list: spelling and grammar. I have mentioned early on that I found a spelling error in a header tag <h3> on my hardest-hit page (-400 positions). I corrected the mistake and within days, WMT reported that the average position of that page had rebounded to #2. This could have been a coincidence, but I do think spelling (particularly in critical places, like title/desc/headers) could be important. That page was unduplicated/unscraped, thick, and had no ads or affiliate links. The page did have a short/duplicate title and description (and was warned for in the html suggestions of WMT), so all three could have caused the page to suffer. Remember that Google told us that with Panda, just a few bad pages can negatively affect the entire site.
[edited by: crobb305 at 12:14 am (utc) on Mar 31, 2011]