graeme_p - 4:09 am on Jan 21, 2012 (gmt 0)

Unless the hit my site took is a complete coincidence, a single large above the fold ad is enough.

I have lost most of my 1st places in the UK SERPS, and the sites that have moved up are Wikipedia (no ads) and a site with internally served ads so I think one way to avoid this may be to sell ads directly rather than use a network.