An interesting developerWorks blog about the benefits of customer engagement via Twitter. The title says it all:? "developerWorks Twitter account saving over $600k per month: what uplift will Google+ provide?"
Interestingly the $600k/month claim comes from what they would have to pay for 200,000 clicks per month through other channels (e.g. paid search).? Of course, this under-estimates the value to IBM, because twitter accounts like @developerWorks build rapport and trust with customers and partners (I'd call that engagement, but marketing professionals might disagree). I'd not have even thought of quantifying the value of a twitter account in this fashion, but I'm going to change my calculus in the future.
When I worked at a BPMS vendor we added partners and some customers to an internal technical mailing list.? The level of engagement with these techies was much improved, and helped convert skeptics into advocates of our company and products.? This was in pre-twitter days.? I'm not sure the effect on twitter is quite as strong per person, but like the mailing list, it can humanize a company and a product, and it exposes customers to your professionals and experts.? That has to be a good thing.