Rob Galbraith has a nice summary of the need and limitations of these new 30MB/s SD cards from SanDisk.  He points out that the cards were designed to compliment the D90’s need for speed and will only function in other DSLRs as 20MB/s cards (the cap for SDHC).

SanDisk’s press release details further:

SanDisk Corporation (NASDAQ: SNDK) today set a new speed record of 30 megabytes per second1 for SD^TM flash memory cards with the introduction of the SanDisk Extreme® III 30MB/s Edition line of SDHC^TM Cards. The new cards, expected to be available worldwide in September in 4-gigabyte (GB)2, 8GB and 16GB capacities, are designed to deliver peak performance when used with the new digital single-lens reflex (DSLR) camera, Nikon D90.

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