We've just started using Twitter. So far it's been create for stitching the company together, we're based in different places and travel a lot. We're a b2b company so we haven't seen many customers on but there are a few thought leaders on - we'll see what happens over the next few months.
I was initially worried about competitive intelligence leakage - if I'm in a particular area that would be interesting to competitors. But I don't worry about that much anymore - I can always protect my updates if I get concerned.
We do have a company Twitter account which we'll be using for announcements to customers.
For the moment, it's more than proved it's worth as an internal tool to help everyone get to know each other, even over physical distance.
twitter.com/simoncoles