Flash storage for gadgets, mobile devices and camera's not only have become larger in storage size, but much faster as well. Both factors are needed to store the plethora of photo's and video's in the extremely high resolution offered these days. And yeah, obviously they needed to become faster to be able to catch photo's in very fast burst rates.
There's another factor though, for the folks with HD camera's the ballgame changed as well, recording 1080P at high quality just requires really fast writing memory. For example 1080p videos at 50fps in the AVCHD format would use up to a bandwidth of roughly 28Mbps (or 3.5MB/s). If you record in Blu-ray format at 40 Mbit/sec you'll already need a card that supports a sustained write speed of 5 MB/sec.
Portable flash memory has become a thorn in the eyes of many though as there are way so freakishly many formats -- and that makes things very complicated for you, the end user. Some examples: you'll see large CompactFlash cards up-to small xD cards. The most common format however is Secure Digital (SD), but that one has multiple formats within its genre as well - SDSC, SDHC, SDIO, and SDXC and these again come in multiple form factors (standard, mini and micro) with a performance rating as well.
The vast majority of SD cards we all know and use the best are the ones that are roughly postage stamp sized, you know these as SDHC (Secure Digital High Capacity) typically ranging from 2 GB to 32GB in storage sizes with a classification hat represents the speed. Very boldly the classification can be translated this way: 6MB/s is a Class 6 card. A Class 10 card has a minimum sustained write speed of 10MB/s. Sustained wsrite performance is what you are after if you use these cards for photo and video camera's.
So class 10 was the top dog, but technology advances fast and if a class 10 SDHC card isn't fast enough for you then Patriot now offers a SDHC UHS-I card.
Patriot Memory announced the EP Pro SDHC/SDXC UHS-I flashcards, these are designed with high definition video and photography enthusiasts in mind. They offer advertised read speeds of up to 90MB/s and are capable of recording at 4k resolution for HD content creation.