Why Register?
Subvein is a game made of love, not greed. I'd rather you introduce 10 more friends to the game than register. Having said that even coders need to eat and registering is a great way to support the development of the game. When you register your account not only are you supporting the game, but your contribution is recognised by the community.
A registered account will unlock a number of cool new features. These features don't give you an unfair edge against unregistered players, but rather will give you an identity within the community and greatly improve your overall playing experience.
However as Subvein is not complete, you cannot register just yet. Registration will become available when version 1.0 is released. So until then you're not missing out on anything! If you still want to support the game all you need to do is tell you friends. I also encourage you to suggest ideas in the forums and submit quality maps for inclusion in upcoming versions.