As of now there are not many consumer products, aside from a few smartphones (and the GoPro HERO3+ Black Edition), that can shoot 4k video. However the SD Association's announcement of new Ultra High Speed Class 3 (U3) card labeling anticipates it becoming more common.

It's mainly been a format for more expensive pro-level equipment because of infrastructure bandwidth, but by guaranteeing a write performance of at least 30 MB/s of constant minimum write speed (or 240 Mbps in bitrate terms), it will be easier for customers to know which cards are fast enough and potentially make shooting 4k more accessible.

Are you currently shooting 4K video? What do you think of the 4K format?