I just looked at a chart covering the past 12 months that shows me how well traffic from Google converts and it's a steady downward slope per 1000 unique visitors.
#1 My site itself holds the reason for fewer conversions
#2 Traffic likely to convert isn't finding its way to my site
#3 People are buying less in general, on average
#4 Change in my rankings for any given keyword.
#5 add your reasoning here
Of interest, the traffic I received from Bing and from Yahoo both followed a different slope which is trending higher, up 2.2% over last year instead of down 12% for Google.
Is anyone else seeing any discrepancies in search visitor conversion rate between the big 3 engines?