Where does it say in Twitter terms of service that it must be used to have a conversation?
Why do "social business people" insist on saying - that a business using it to post a press release is just wrong.
So, yes - I believe small and large businesses can have a Twitter profile that does not engage but purely posts offers, jobs, property for sale... however I would like to see in their Twitter profile "Bio" that - "this account is solely for the use of posting jobs (etc), if you wish to speak go to: phone, email, the bosses Twitter account..." I would also like to see more businesses state when the account is most likely to be in use. A great example is the Poppyscotland Twitter account web page - they've created a web page that not only shows the users of the account but also that its use is Monday to Friday 10am to 5pm: http://tinyurl.com/twitter-ps. Agreed this does not suit everybody but they've laid their stall out stating quite clearly their intentions and how they wish to use it.
Are you a business with a Facebook page - do you have a terms of engagement page? Do your "Like'rs" know that a comment is likely to be deleted or blocked if they post inappropriate links or competitor deals - don't you think it's about time you added one - here's an example of the one on Braehead's Facebook page: http://tinyurl.com/braehead-rules.
Set your stall out - be clear about what your customers or clients can expect - they're not mind readers!