Thanks for the response, @cbsembler!
I hadn’t seen that post on the Ideas form yet—glad to know there are at least a few others thinking about this issue. I just up-voted that one and I’ll add a comment shortly.
I should elaborate a bit more on how I’ve been handing repeat customers: I’ll have a contact property of “last purchase” that syncs up with our shopping cart to add the product code of the most recent purchase. Then I can build a list for a given product by looking if that contact property has ever contained the code I’m targetting.
That approach works well for workflow goal conditions and general list building, but I still wish I could do a Marketing Performance or Contact Lifecycle report where each stage could be defined by membership in a particular list. I’m hoping the custom reports tool will eventually get there.