What is USB Type-C ?

USB type-C is the new hot industry standard connector and cable used to power the new MacBook. The USB-C connector was developed by the USB Implementers Forum, the group of companies that has developed, certified, and shepherded the USB standard. It counts over 700 companies in its membership, including Apple, Dell, HP,  Intel, Microsoft and Samsung. This is important, because it's more likely to be accepted by the majority of PC manufacturers. Contrast this with the Apple-promoted (and developed) Lightning and MagSafe connectors, which have limited acceptance beyond Apple products.

So, is it like the Micro USB?
Yes, the USB-C connector looks like a micro USB connector at first glance, but it's slightly thicker to accommodate its best feature: like Lightening and MagSafe, the USB-C connector has no up or down orientation: as long as the connector is lined up right, you won't have to flip the connector to plug it in! The cables also have the same connector on both ends, so you won't ever have to figure out which end to plug in, unlike the older USB cables we've been using for the past 20 years.

Is this USB 3.1?
Yup, this is USB 3.1, which is theoretically twice as fast as USB 3.0.
It's fully compatible electrically with USB 3.0, though obviously it won't plug in physically without an adapter. By the way, it's about as fast as the original specs for Thunderbolt (10Gbps).

What about those adapters?
The MacBook doesn't come with any adapters aside from the charger and a single USB-C cable. Others will be available separately. Apple's USB-C to USB 3.0 adapter will be $19, but the one that will give you the most utility is the decidedly expensive $79 USB-C AV Multiport Adapter , which gives you USB 3.1 Gen 1 (the old connector), USB-C pass through for charging, and an HDMI port. Since USB-C is an industry standard connector, cheaper adapters are inevitable.

What else does it support?
The USB-C connector in the MacBook supports DisplayPort, HDMI, power, USB, and VGA. Notably absent is Thunderbolt, which is superseded by USB-C just as FireWire was replaced by Thunderbolt .
USB-C to Ethernet is a no-brainer, but you may have to daisy chain an older USB-to-Ethernet adapter to your USB-C adapter for the time being.

Image courtesy: AnandTech