Simsi - 3:43 pm on Oct 29, 2008 (gmt 0) [edited by: Simsi at 3:43 pm (utc) on Oct. 29, 2008]
Have you considered the fact that Google has done more on geo-targetting of SERPS for people from different countries? For example, if you are in the UK and you are searching on Google.com, you will possibly see a very different set of results to someone in the US also searching on Google.com. So it's possible that you think your rankings are back where they were, but it may only be that way if you live outside the US (example). The Adwords Preview tool will allow you to check out the different result sets to confirm.
[edited by: Simsi at 3:43 pm (utc) on Oct. 29, 2008]