A picture says a thousand words: dashboard screenshot
This is a side effect of setting all the font sizes (and many other elements) in fixed px units and relying on those sizes to get the desired visuals. Those of use who need larger text sizes end up with a broken layout. I think WP has always used fixed font sizes, but it never caused this bad of a problem before.
Changing the admin CSS to use relative font sizing instead of fixed px values will easily correct this, but now I have to go through the trouble of making a whole plug-in just to fix the flawed styling. It's ironic that 2.7 is touted as focusing on the user, but you really missed the boat in this respect. And it is so unnecessary. (heavy sigh)