You may have noticed recently, if you're a Google+ member, that both Jeb and Notch have released a preview screenshot each of some things they are working on. Above is the screenshot that Jeb posted on his Google+ profile. It not only shows ruins, but also new blocks! I had the pleasure of talking with Jeb and the stone blocks are new, and do not replace any existing blocks. As well, there are metal gates! The full-sized picture of that can be found here.
This screenshot, posted by Notch on his Google+ profile, shows many things! The first and most obvious being the buildings. No doubt, these are to be for the NPC villages which are in the works, as said on Notch's blog. Also pictured are what seems to be giant mushrooms! Notch has indicated that he's hoping for them to have their own biomes, though there is no confirmation as to what their uses will be for.
With all of this said, 1.8 is shaping up to be quite the update and it seems that it is going to greatly change Minecraft - for the better. There will be a lot more interactivity and things to do, resulting in a better experience for everyone.