Nokia's firmware officially supports a 24mhz bus for SDHC cards. Philip Langdale created a patch that clocks the bus to 48mhz to utilize the full potential of high speed SDHC cards. Nokia and TI said the reason they didn't clock the bus to 48mhz is because they saw issues with it implemented. I don't know what the issues were, but it seems like plenty of people here have used the patch without issues. The read speed for the cards almost doubles with the patch. You can see some speed tests here. Some more info about the patch and a link to download are here. I'm planning to boot from my SDHC card and hope to see improvements in boot times and overall system performance. Search the forums for "48mhz" if you want to read more threads about it.