I've been hanging out on the microformats.org discussion list related to product data - too bad the email list isn't linkable. Anyway, these are my latest thoughts:
I am also wondering where and when a microformat for products would be useful. I'm generally wondering when /microformats/ are useful. (see http://microformats.org/about/) It seems to me that general narrative text and general conversations in text sometimes have 'hard' data like people, places, dates, times, phone numbers, etc Marking these as /being/ people, places, dates, etc. makes it easier for software to process - but the underlying data below the markup is still readable and sensible to people. Product data isn't like this at all. It's an unregulated mass of named properties with little rhyme or reason - there is no need to gently superimpose tags without breaking the elegance of the underlying data because there simply isn't any underlying elegance.
What it sounds like may be useful is a simple way for people to talk about things and reference those things, but without needed to fill in the blanks for unnecessary detail. For example, if I talk about the new mountain bike that I bought and immediatly scratched up by tipping over, it would be cool if I could tag the phrase "new mountain bike" as a reference to a product - but I don't want to actually describe the composition of the bike, the kind of tires and suspension and whatnot. People don't do that, manufacturers do.
If we want to solve this for manufacturers, then just use XML. Then the next problem is how can software determine which attributes from which manufacturers mean the same thing? That's where a shared 'open product attribute' database would be useful.