Showing support on your sleeve -- while fairly trite since you're only updating your status -- makes sense to me. What doesn't make sense to me are the brands that feel the need to insert themselves into the conversation surrounding a tragedy.
There are a lot of articles out there about how to effectively use social media to enhance your product or service. Foursquare, Google+, Pinterest -- there are so many it's dizzying. Plus, all the time I'm spending promoting our work seems to be taking time away from client relationships and sales.