A class 10 card is supposed to have a minimum of 30 MB/sec write speed.
I know it's relatively late saying this but for the benefit of those who aren't aware, I have to correct you there. In the context of SDHC cards, Class 10 specifies a minimum write/read speed of 10MB/s. It's just the case that the Sandisk SDHC card you mentioned can write at a maximum write speed of 30MB/s (albeit only in short bursts), which of course is a good selling point and beneficial to those recording HD video at a high bit rate or large RAW + JPEG files.
As you hinted, the write speed of the faster SDHC cards can become redundant with photos because the camera's buffer may choke at a lower transfer rate than the SDHC card's maximum transfer rate e.g. if the buffer can write no faster than 25MB/s, a 45MB/s Class 10 card will be no faster than a 30MB/s Class 10 card with photos.