We got together and bought Carl WA3SEE a K1 kit as a retirement present. He spent the rainy/windy days caused by Hurricane Irene building it, with a few missing capacitors and a bad xtal slowing him down a bit. But it worked fine on the bench.
Yesterday, Carl and I hike the Appalachian Trail in MD with the K1 and operated from Lamb's Knoll, an official "summit" as defined by the Summit on the Air folks. A blog post with more detail can be found here.
As a satisfied K3 user, I was really impressed with the K1. Compared to past QRP rigs, the receiver was just soooo quiet and sharp.