Domains are very cheap currently, the only "official" domain that is owned by Notch is minecraft.net, the rest of the domains are owned by me. I currently have:
minecraftforum.net < This forum, the domain that it runs off.
minecraftforums.net < It's a forwarder to minecraftforum.net, in case people typo or think it's "forums".
minecraftskins.net < Skin site
minecraftwiki.net < Minecraft Wiki, I "own" and host it, but Quatroking is the main administrator who contributes the most.
minecraftmaps.net < Minecraft maps database that I've yet to start/complete.
I personally prefer having a full domain as opposed to a subdomain, it would have been possible to get set up with forum.minecraft.net, but Notch would have needed to **** about with DNS records and it can be a pain.