While some people are clamoring for higher-capacity SD cards, few need--or want to pay for--the extra video-recording speed. Panasonic, for example, will be issuing its first 64GB SDXC as a Class 10, 22-megabyte-per-second version card for almost $600; however, SanDisk announced its first 64GB card at a slower Class 4, 15MBps for the more attractive price of $349.99.
True, only products announced since January--and only some of those--support the new SDXC standard, but even in a lot of the newer cameras and camcorders, Class 4 is sufficient for video recording. However, that 15MBps speed might slow you down when bursting in a midrange dSLR, which increasingly support SD media. Overall, I think going for the slower, cheaper memory is the right move for most people for now. Furthermore, if you just bought a brand-new, SDXC-supporting device, you can get that extra capacity today. According to SanDisk, it's shipping the cards now. I believe makes it the first SDXC card available, despite prior announcements from Panasonic and Toshiba.