The website has opened for business:
https://eforms.homeoffice.gov.uk/out...er_scheme.ofml
The preferred entry point is actually here:
https://www.gov.uk/registered-traveller-scheme
It is currently for the restricted list of users (existing Iris users from "5 Eyes" plus Japan) and free at the moment, from April 2014 there will be a fee and my understanding is that by or at that time a wider group of travellers can use the system. And the process basically allows qualified passengers the "shortest available queue". From April it will allow biometric passport holders to use the e-passport gates.