I found two twitter clone makers http://www.floopo.com/ and StatusNet (used to be Laconica) http://status.net/?source=laconica. Floopo appears to be simpler to set up. Which one would you choose?
Top 250 twitter clone sites http://www.honeytechblog.com/top-250-list-of-twitter-clones-sites/
There is a blog called "What did you buy today?" http://www.obsessiveconsumption.typepad.com/ but I couldn't find a twitter clone answering to this question.
Of course, Twitter is already used to share shopping news: http://twitter.com/#search?q=bought so there may be a use for a specialized status update for shopping.
Thank you.