Unfortunately you mostly have to wait when it comes to Maemo itself and to getting packages provided by Nokia, but you can track development of some of the open official Maemo modules either in gitorious.org or in garage.maemo.org. I think a problem here is that "normal" customers/users could run into serious issues if Nokia provided unstable builds that e.g. destroyed data. So in the end it's about legal issues, I guess, plus a slow change from classical cooperative workflows to more open workflows, with all its related internal discussions. If you love to test bleeding edge 3rd party software on the Maemo platform then http://wiki.maemo.org/Extras-testing could be interesting for you. (The traditional warning: That software might brick your device, eat all your data and kill your kittens. All on your own risk.)