tedster - 5:58 pm on Dec 28, 2011 (gmt 0)
You can sometimes get a clue by using the Google Search Tool called Verbatim Search [webmasterworld.com]. It removes all the personalization and semantic "adjustments" from the results and gives you a strict interpretation of the SERPs for your query term.
My suspicion is that a true penalty will still lower your rankings in the Verbatim Search results. But if your site lost rankings due to a change in the algorithm [especially the kind of "mind reading" that search engines do today, then Verbatim Search often shows your page near the position you saw before the ranking loss.