SE will be doing this on the smaller sites eventually. And well, some of the issues with it feel feels a bit like
It also actually takes up less vertical space and uses horizontal space better (It dosen't use more, but moves things around a bit. Feels bigger to me)
And probably brings with it customisable tabs (and I will certainly be complaining loudly if we don't).
There's a bit of a learning curve (and when this hits SU, If the TPTB don't, I'll probably dig through and do a quick meta post on this - and if it hits here first, I might try it here first) but "disgusting, unergonomic, suboptimal. And it is fixed to the top" is 3/4 unclear and 1/4 wrong. If there's specifics you are unhappy with, go tell SE on MSO. We're pushing for a few things we need like help links on the top bar for all users
Now, I don't like the newfangled white theme, and some sites are going to be a agony in the donkey to do but this seems a bit hyperbolic.