The SD Association today defined a new specification for very fast SDHC and SDXC cards. Ultra High Speed I (UHS-I) will guarantee a maximum interface speed of 104MB per second, or four times the 25MB speed of regular cards. As long as they're used with cameras, readers or other devices that can recognize the speeds, UHS cards should have no trouble recording HD video or shooting continuous RAW photos.
It wasn't mentioned when UHS-I cards would reach the market, but the Association considers the labeling a green light for cards based on the faster technology to reach the market. Using the full speed will also require host devices that are still currently rare, as even SDXC readers won't necessarily address the faster speed.
Source: electronista
