The problem with such a site is how to get the data? There really is no feasible way. At best you could do an FF extension that could intelligently scrape a purchase confirmation page on a merchant’s website. The problem with this is that there’s no incentive for the consumer to do this. I as a consumer probably would not mind this data to be recorded if it was done anonymously and both the collection process and resulting data set was very transparent. However, it’s unlikely I would actually spend even a couple minutes to make sure the data was recorded accurately. Moreover, FF represents a small minority of Web users and the % who would have this extension installed would be small (there’s no real immediate motivation for a user to install it).

Well, this all changes with Google Checkout. By acting as a payment provider for merchants who use Checkout, Google can record the details of each transaction: what was bought, what price (possibly even what coupons were used?), etc. Voila! You have the data you need for the tool I described above. And because the data is taken straight from the horse’s (merchant’s) mouth, you do not rely on scraping or the user which are flaky. Beyond just the community value, there is also value for the user in that he/she could log-in and see all the purchases they’ve made online and possibly view receipts, rebates, etc. in one spot.

Sound cool? I think so…