Update: TetherMe worked for about an hour, then I restarted the iPhone and it disappeared. I have since tried reinstalling the mobile substrate, preference loader, tetherme, and installed bootstrap, but I can't get TetherMe back.
iFile is now available, and I tried switching back to iOS 7.0.4 and installing (as above), and to 6.1 and installing, but it still didn't work.
Any suggestions how I can get TetherMe working again?