I experienced slow down uploading data into USB MASS STORAGE against SL 9.3.
It's aprox about 70KBps. Syncing is enabled by default. Disabling syncing
manualy helps a lot. On SL 9.3 it was about 600KBps. 
Tried with two devices, I have now only one by hand.

dmesg:

usb 2-1: new full speed USB device using uhci_hcd and address 2
Initializing USB Mass Storage driver...
scsi0 : SCSI emulation for USB Mass Storage devices
usb-storage: device found at 2
usb-storage: waiting for device to settle before scanning
usbcore: registered new driver usb-storage
USB Mass Storage support registered.
  Vendor: USB       Model: BAR               Rev: 2.00
  Type:   Direct-Access                      ANSI SCSI revision: 02
sda: Unit Not Ready, sense:
: Current: sense key: Unit Attention
    Additional sense: Not ready to ready change, medium may have changed
sda : READ CAPACITY failed.
sda : status=1, message=00, host=0, driver=08
sd: Current: sense key: Unit Attention
    Additional sense: Not ready to ready change, medium may have changed
sda: test WP failed, assume Write Enabled
sda: assuming drive cache: write through
sda: Unit Not Ready, sense:
: Current: sense key: Unit Attention
    Additional sense: Not ready to ready change, medium may have changed
SCSI device sda: 511744 512-byte hdwr sectors (262 MB)
sda: Write Protect is off
sda: Mode Sense: 03 00 00 00
sda: assuming drive cache: write through
SCSI device sda: 511744 512-byte hdwr sectors (262 MB)
sda: Write Protect is off
sda: Mode Sense: 03 00 00 00
sda: assuming drive cache: write through
 sda: sda1
Attached scsi removable disk sda at scsi0, channel 0, id 0, lun 0
Attached scsi generic sg0 at scsi0, channel 0, id 0, lun 0,  type 0
usb-storage: device scan complete