Yes, it is "limited" to something like 500mbps. At least the 2013 models got that, this one might be fast, 802.11ac can go faster than gigabit ethernet.
You could spend $12 on a superspeed+ USB-C to USB-A adapter at amazon. But that doesn't get you power.
I predict USB-C high power hubs will happen soon and we'll all be happy.
I was really excited about the machine until I realized I would have to take the dongle everywhere I traveled. I don't want a dongle and I certainly don't want an $80 one. I do want to attach a device and a power cord at the same time.
I would be fine with two ports. I have no idea why they didn't put another port on the right. Maybe to sell $80 dongles?
http://store.apple.com/us/product/MJ1K2AM/A/usb-c-digital-av...
Without it, the machine is essentially limited to wi-fi speeds for everything you try to do.