1.8.1 is out, with fixes for the "shift-click" crashing issue with chests and dispensers! Before the patch was released, user RoosterInASuit discovered a way to customize the new panoramic Main Menu background! The technique is fairly simple and easy to follow - what sort of customized backgrounds can you make?
September 56 2034,The world was hit with a meteor that let out poisonous gasses and every female and male died except for a handful of humans,all of them mutated into horrible creatures except for one male named Steve with only his wits and a handful of logs.....This is his story!
I'm in the same boat. 1.7 had around 20-35 FPS, but 1.8 is yielding 4-8 FPS. Both are on lowest settings possible (1.7's render distance is set to "Normal," however, where as 1.8's render distance is set to "Tiny").
And to make matters worse, it seems as if this problem isn't widespread and, as such, the amount of attention it's getting (both from forum users and Mojang themselves) is nominal at best.