Where should I discuss SD/MMC FAT issues?

[skimask]

Sorry, I forgot to say that I'm using FAT16 when I format the MMC.

That fat32 document has a load of info in it, and specifies where it differ's from fat16...not that it matters much

My application is data recording at about 100 sectors a second.

I was able to shove a bit over 600K/sec into the CF card on my player, but that's using the IDE mode, parallel data transfer. 600K was as fast as the PIC could go @ 40Mhz.
You'll be limited to the max SPI speed, and I think you'll be lucky to be able to handle 100 sectors/second (100 sectors = 512000 bytes = 5.12mbps) and still have any time leftover to do any sort of interrupt processing.

I do have this odd recollection of there being some part of the FAT where data is written LSByte first. Maybe it was the file size?

Do a search for fatgen103.doc and you'll see what I'm looking at.
And yes, offset 28 is the file size, and yes, it is LSB first...little endian...