The very cool Field Museum in Chicago will get a Wi-Fi network, built by Concourse: Most users will pay a "nominal" fee to access the network, but Chicago Public School kids and their teachers will get free access. The museum also envisions using the network to offer interactive exhibits in the future.
The Experience Music Project, Paul Allen's music museum in Seattle, also built a Wi-Fi network in its space recently. The networks sound useful internally for museum workers as much as for an extra service for visitors. I'm not sure how willing or interested I would be in paying to access a Wi-Fi network in a museum after I've already paid an entrance fee. But the networks would offer a great conduit for delivering content about exhibits to handheld devices as part of the regular museum experience. The EMP has a bar and restaurant that people can visit without paying an entrance fee to the museum so those users might be interested in paying to use the network.