A MiFi is a nifty little device you can get fromor here in the States. It receives a cellular data signal and then rebroadcasts it as a Wi-Fi connection.
However, one annoying thing is that when you plug it into a USB port, it insists on acting as a modem instead of a Wi-Fi access point. This means that you can't charge it from your laptop and share it the data connection. I ran into this issue at an airport when I wanted to charge the MiFi and share with my colleague, but I couldn't find an electrical outlet.
Thanks to Allison Sheridan at the NosillaCast Podcast for the solution.
Since the MiFi is a router, you just need to.
Log in to your MiFi at 192.168.1.1 and click on advanced, and then on config file.
Download the configuration file. Knock the .sav extension off when you save it.
Open it in a text editor.
Right near the top of the file you'll see an entry called routeroverusb. Change that bit from a zero to a one.
Now save the file.
Go back to your router screen, browse to the config file, and upload the modified file.
Your MiFi should act no differently when plugged into your USB port than when it's not, except it will still charge.
This only works on the MiFi 2200. If you're in Europe, you may have a different model. For those folks, Allison suggested getting a charge-only USB cable, missing the pins for data communication, preventing your MiFi from acting all modem-like.