We've experienced extreme hills for a long time now. They're dramatic, though awkwardly formed, almost as a geographic phenomenon exclusive to Minecraft. But we've never seen a true Mountain. A sequence of triangular rises, green at the base, grey up the center, to a singular snowcapped point (or series of points). Extreme hills can only allude to this, seldom does anything about them truly evoke a sense of a genuine Mountain. Right now is the time to finally bring proper Mountains into Minecraft. If Mojang doesn't try it now, it will be a severely missed opportunity. Because if it's not going to happen now, in the 1.7 "Biome Update", we all know we can kiss the idea goodbye for another two years.
It seems like a fairly natural looking mountain to me (minus the little floaty bit at the top)
My Survival Journal