My colleagues at Shopster [http://getshopster.com/] are implementing really awesome indoor navigation project with 300+ beacons installed in largest Russian mall. See demo: http://www.youtube.com/watch?v=VAM4bJst2Jw

And yes, we built custom beacons on top of OpenWRT routers & USB dongles –> hence high frequency updates, high power & no battery dependance. Also we built a mechanism that allows us to update majors/minors/uuids so that no external party can use our beacons.

Battery beacons are only usable for a couple toy usecases in my opinion.