Thanks for posting this questions. I'm sure some of our client within the healthcare vertical would have some great feedback. We have multiple deployments of online communities (public facing), as well as internal employee collaboration networks.
Based on their security needs, our clients can host SBS internally behind their own firewall or we can simply deploy their instance via an enterprise SaaS solution with Sungard. Either way, strict security standards are easily addressed.
Financially though, more and more organizations (including those in healthcare) are investing in easy to use social collaboration platforms because these types of tools are meant to fix existing business pains and in the end save time and money. Having users who can't find content or have meaningful conversations around specific content, having users that can't find experts they need and living out of email, having users that can't stay in touch while mobile or that can't find a way to work out of one solution instead of 10... these are just some pains that SBS aims to address among many other issues.
Feel free to take some time to explore some of our customer webcasts in which they talk about their own use. There is even one from the Air Force Medical Services:
Hope this helps, but again, I'm sure other users will have great feedback as well.