I have a flash drive with two partitions:
sda1 - 4GB (3GB free) - EXT3
sda2 - 2MB (8KB free) - FAT32
@nolanlawson tried to use it with Tessel.
Tessel decided to mount /mnt/sda2, but didn't touch sda1 at all. I would expect it to mount both. Or maybe the biggest. It's a corner case, because most people will only have one partition, but it would probably be good to know what's up (or understand/document the behaviour).