Anybody using Posterous? Can you advise me on its value?

I do PR for a small nonprofit, a conservation organization. My outreach includes social media such as Twitter, Facebook and YouTube. We also have a fairly nice website that I keep up-to-date. We don’t blog because our small staff doesn’t have the time or willingness to keep a blog current.

I’m always open to other ways to let people know about our current activities, related groups’ work, etc. They need to be easy to update and user-friendly. Recently, I’ve read a bit about Posterous but I’m uncertain whether it would complement or just duplicate what we’re doing already. I can’t get a feel for it from the informational pages available and I am reluctant to sign up for yet another account that I won’t ultimately use.

Have any of you used Posterous personally or for an organization? How do you like it? How do you use it? Are there similar services you like better? Would it even be useful for an organization like mine?