My own thoughts:
CPU-speed: Not a huge leap forward. My guess is 10-15% improvement - I think Apple will do anything they can in regards to battery life and maybe down-prioritize CPU-performance a bit.
GPU-speed: Radically increase. Intel has talked about major leaps. My guess: 60% faster graphics.
SSD-speed: Bumped from 500 to 600-650MBps read. Not a lot.
Temperature: Inspired by the rMBP? Is there enough room for new kinda vents/asymmetrical fan?
Hours/Charge: Big, big, big one. Current MBA is just under 7 hours. I think Haswell will be at least 9 hours/charge.
Screen: Unfortunately, I think the screen will remain the same. No rMBP. I think the 13 MBP will get retina, and if the MBA follows, they will overlap too much into each other's segments.
Design: The same. Nothing spectacular (certainly not a redesign)
I'm genuinely interested in your thoughts, and if you think I'm wrong (I most possibly am
), please, tell me (why)!