If you want to engage your business through the people at the business and those people would be using twitter/facebook/etc then yes, you should have a twitter account. But only if those people are interacting with your product on their computer already.
I.e. we sell software to other businesses. Those people using that software are on their computer and tweet us, send us email, probably check their facebook, etc.
But if you are selling steel manufacturing machines to other companies, don't waste your time.
The people who sell laundry services to my building are on facebook and I don't believe their effort/time is being well spent. We use the laundry service because our building owner chose it, and I guarantee you that he didn't choose it because they had a facebook fan page.
However, it does work extremely well for them for customer service. If you can provide customer service that way for your product, then go for it.