I have been having a few issues with my MiFi, in the main it keeps dropping connections and failing to allow devices to connect.
Now I think it is a battery life issue, once the device runs out of power, it drops the 3G connection and the wifi stops working. The lights on it are never that clear about what the status, but the browser configuration (once connected) seems to work fine.
Now my MiFi is an original Novatel model and I’ve not updated any firmware since I got it, so that’s on my list of things to try.
Generally though when it does work, it works a treat. I also like that if push comes to shove I can use it as a 3G dongle via a USB cable.