iFixit finds that not much has changed with the MacBook Air. The new Broadwell processor doesn't change much in terms of capability, though iFixit notes the chip can expect power efficiency gains of up to 30%. Additionally, the MacBook Air remains Apple's only glue-free laptop.
The real changes have come to the new 13-inch MacBook Pro. The major change with the Pro was the addition of the new Force Touch trackpad like the one found in the new MacBook. iFixit dug into the new trackpad, getting a look at the the electromagnet that powers the pad's Taptic Engine. From iFixit:
The magnets rapidly push and pull against a metal rail mounted beneath the trackpad, to create a tiny "buzz" of feedback with each click (and a second buzz for a "force click").
For the rest, most of it is what you would expect to find in a MacBook Pro, including the Samsung flash storage, DRAM, and flash controller units. The unit iFixit looked at had an Intel Core i5-5257U processor, along with an Intel Thunderbolt 2 controller.
You can read more on these latest tear downs from iFixit at the links below.