hi Graeme,
you can start studying TTCatalog sample project that comes with three20 library.
Right now I'm working with a improved version of the three20 made by Rodrigo Mazzilli, you can find it here (http://github.com/rodmaz/three20).
rodmaz's version is a fork from the original project and it comes with some improvements, specially in TTLauncherView. It has a new class called TTLauncherViewController which is easier to use, take a look at his demo project TTCatalog.
http:// three20.info/ is a good collaborative site with some tutorials, but it doesn't have much information about TTLauncherView at this moment.
Finally, you should join three20's google group at http:// groups.google.com/group/three20 where you find hundreds of developers using this library.
best