I'm in the middle of a terrible experience with C4 as well. I ordered a set of USL 3.0 wheels and this is the series of events:
April 15 - Order placed
May 1 - Wheels shipped
May 15 - Wheels received
May 15 - Cassette and tires installed. Rode up the street (maybe 200 feet) and noticed something was not right, rear wheel was wobbling. Took the bike back inside, inspected real wheel, found that the axle was bent.
May 16 - Confirmed at bike shop that the axle was bent - http://www.youtube.com/watch?v=yGOZN1Mnchs
May 18 - New rear axle assembly shipped
May 25 - New rear axle assembly received
May 31 - New axle assembly installed
June 2 - Went for a 128 km ride (rain for ~30 km). When cleaning bike after, noticed wheel was not spinning smoothly and the same wobble was happening.
June 4 - Took wheel to shop, confirmed that the axle was bent, and the bearings were rough / seizing.
June 5 - Rear wheel shipped back to C4
June 8 - Rear wheel received by C4
July 10 - Rear wheel shipped to me
July 17 - Rear wheel received
July 20 - Cassette installed on rear wheel
July 25, 26, 30 - Rode to work: 45km round trip
July 30 - Took the rear wheel off the bike and found the axle to be spinning very rough, I assume the bearings are seizing.
Talked with Mark on the phone about two weeks ago and he wanted me to test a new hub, with a 17mm axle that is 30% stiffer than what I have. I politely declined and asked for a refund, which he reluctantly agreed to. I've since sent three emails, and one voicemail confirming the address to return the wheels to with no response.