Just dusted my Pineapple off today to try it out with a USB 3g dongle - first thing I did was update the firmware to 2.7.5.
After about an hour of futzing around with the config I went into the shell and ran the usb_modeswitch directly. This is what I got: usb_modeswitch: can't load library 'libusb-0.1.so.4'.
Hope that helps!
knotworx