Upper-tier companies can use it to monitor their products and services. In this way it can be used to learn how your customers regard your products, if those customers are experiencing problems and Twitter can be used to mitigate complaints by responding directly to a customer with a complaint.

Small businesses can definitely benefit by promoting their brand and keeping their products and services in the mix of their competitors.

I have a client that has begun using it – taking pictures of cars that he has worked on – when potential customers begin searching on Google, Bing or Yahoo, those twitter updates will begin ranking high on search engines, not to mention other learning about his service without digging through search engine result pages.