A few businesses caught the idea early on, such as woot.com. Woot.com’s implementation, to me, seems like the ideal way to use Twitter (or RSS feeds, for that matter) as a marketing tactic. Of course, part of this is due to the nature of woot.com’s concept: sell only one item a day, at a discount, until midnight or it sells out, whichever comes first. Thus, one update a day keeps you informed of the best deals.
For other companies with wider offerings, this might be a bit more difficult to do, but then again, if you can subscribe via RSS feed to search results pages on blogs, why not on shopping sites? Tamar Weinberg covers more of the best business uses for Twitter today in Can Twitter Serve as Highly Targeted Marketing Tool?
TechCrunch also has an article on more ideas on how to take advantage of Twitter and the latest changes to the Twitter API.
So go get Twitterpated!