Dell's 600,000 followers on Twitter (@Delloutlet) have earnt it more than $3 million in sales over the past two years, the company claims. $1 million of that has been in the last six months.
That works out at about $2 per follower per year. Not bad cash, if Twitter was tapping into it, which it currently isn't. The numbers are able to be tracked because Dell issues discount codes, which the company can add up the sales from.
Of course, there's the question of how many of the people who used the codes would have bought a Dell even if Twitter didn't exist, or whether the codes were spread more widely on deals sites, but even so, it's a good source of revenue.
These are also US stats. A similar Twitter account is in place for Dell UK (@DelloutletUK) but the company hasn't published any stats as to how well that's doing.