@nutter: I'm relatively sure that it happens on the SD card itself. If I understand correctly, even the SD controller on the N800 doesn't have to know anything about the actual mapping of physical blocks to logical blocks. AFAIK, the only thing really needs to be avoided are lots of small writes, since every time 1KB is written a whole block gets erased and written. Better to wait and do 1 64KB write, than 64 1KB writes. BTW, thanks for the work on tile based storage.

-John