You can find it on the left menu, under My Ancestry as, not surprisingly, "Ancestry Composition" .
I put a bold black and red box around the My Ancestry section
Here is what my Chromosome View of Ancestry Compostion looks like as of Jan 15, 2013. Set to "sub-regional" and "speculative":
Another view, called Split View is available *IF YOU HAVE AT LEAST ONE TESTED PARENT AT 23ANDME*
They have apparently designed the new Ancestry Composition to improve as they gain more samples, so we can look forward to more precise and accurate results over time. I hope they also add the start and stop points of each segment.