Per the SDcard.org site:
The next-generation SDXC (eXtended Capacity) memory card specification, pending release in Q1 2009, dramatically improves consumers’ digital lifestyles by increasing storage capacity from 32 GB up to 2 TB and increasing SD interface read/write speeds up to 104 MB per second in 2009 with a road map to 300 MB per second. SDXC will provide more portable storage and speed, which are often required to support new features in consumer electronic devices and mobile phones.
A 2 TB SDXC memory card can store 100 HD movies, 60 hours of HD recording or 17,000 fine-grade photos. Faster bus speeds will enable professional-level recording in compact consumer camcorders and increase the number of frames shot in a second with SDXC cameras.
The faster bus speeds in the SDXC specification also will benefit SDHC, Embedded SD and SDIO specifications.
Mike (Thanks to Andre)