If you don't engage in multiple back channels, you may not see multiple use cases. Different tools are best for different types of interaction. Just because post-it notes didn't work at WebWise doesn't mean they don't work in galleries... as we know from the success of many talkback boards.If you ask visitors/participants to try a new tool, make sure it has as low a barrier to entry as possible. I have yet to see a museum set something up that is as simple to use as Today'sMeet.If discussion is the goal, you don't need user profiles - you just need a way to talk. If building up a personal profile/relationship with the institution is a goal, people need to uniquely identify themselves.Think about the possibility for asynchronous back channels that allow visitors (and staff) to share deep content with each other over time. Consider, for example, the rich conversation on Flickr about this image from the Chicago World's Fair. You could imagine a comparable conversation available to visitors onsite alongside exhibits or artifacts in the galleries.If possible, find ways to show the real-time location of people who are engaging in the back channel. The Mattress Factory's new SCREENtxt application uses a location-based system so that visitors can identify whether other participants are onsite at the museum or not.Make allowance for emergent back channels that visitors/users "bring with them" to the experience. These tools are particularly valuable for the "portal to the world" back channel use case. Every time I see a kid take a cellphone photo in an exhibit, I know that photo will immediately travel to Facebook, Flickr, Twitter, etc. How can your system capture that activity?