Minecraft 1.6 is taking steps towards Mod API support, and today it took a bigger one. Minecraft 1.6 will no longer support the texture pack format in Minecraft 1.5 and below, and will replace it with a more advanced format called 'Resource Packs'. Resource Packs is a new format designed to allow changing a larger number of Minecraft features without modding, such as changing the textures of blocks (like a texture pack), changing game sounds, changing game fonts, and much much more. Nathan Adams at Mojang said:"As an essential step towards the Minecraft modding API, and also for sanity's sake in our own code, we're removing Texture Packs and replacing them with a new Resource Pack system. Ultimately, every mod/plugin will be its own resource pack, vanilla will be a resource pack by itself, and users will be able to apply multiple resource packs at once."
Are you looking forward to the new customization opportunities, or are you still rocking a discontinued texture pack from Minecraft 1.4 that you can't give up? Either way, you might be glad to know Mojang is working on a 'converter' for Minecraft 1.5 texture packs.
Source: Github