Twitter - thumbs up.
We've been using it at work to post up what's going on to a private user id for the company. It usually has fleeting field reports while we are onsite of the mostly useless (dinner/tea postings) variety, but helps stay in touch when you are out and about.
There's an iMac in the kitchen running TweetDeck that shows the posts, and has additional columns for things like company mentions in the press, competitor mentions, partner mentions, etc.
The Twitter website is a bit limited, but get a good API client like TweetDeck and it becomes a lot more useful. You can add in Facebook streams as well, but you need to try and filter out shite like Farmville/Hearts updates to keep it clean.