As the retail channel becomes more considered as a communication channel the need for metrics to measure its effectiveness increases. Brand marketing people like measurement and they want to see the same kind of measures that are available for other media.
Two different initiatives are being developed to deliver this:
MARI (Marketing At Retail Initiative) is being developed by Sheridan Global in conjunction with POPAI. Sheridan Global provide the technology and analysis for what they have described as a large scale syndicated qualitative piece. The focus of this is on shopper engagement. How much do shoppers see the marketing material in the store and most significantly how much do they pay attention to it and ultimately buy the product?
This initiative really focuses on the success of different in-store executions in engaging shoppers. Consider it the Millward Brown equivalent for in store.
MARI has been initiated in a few markets including US and UK. A good white paper on it is here: http://blog.broadsign.com/digitalsignagedigest/wp-content/uploads/2007/12/mari_usa_white_paper.pdf
P.R.I.S.M. (Pioneering Research for an In-Store Metric) is being developed by Nielsen in conjunction with the In Store Marketing Institute. This is much more focused on providing a media metric and involves a lot more robust traffic counting within stores. So far work has only been done in the US. This aims to provide measurement for instore media. Consider it the in store equivalent of Nielsen ratings.
A good presentation providing an introduction and analysis of early results is here: http://www.instoremarketer.org/article/analyzing-PRISM-data
And a good evaluation of the impact of PRISM here from Shopper Culture: