One user is on the verge of offering a full size SDHC slot for the N810 that will fit inside the case with a modified (and supplied) back cover. This would allow 32gb of storage now and (if you can afford it) 64gb later this year (according to reports).
See this thread:
http://www.internettablettalk.com/fo...ad.php?t=23205

BTW, I don't think there are 64gb micro sd cards availble - I think 8 is the largest but I could be wrong.
BTW2, you know the N810 takes miniSD (and microSD with standard adapter) but not full size SD as purchased.