I've tested it using a usb 3g modem (sun bro). Works great and not that difficult to configure. The program has a small PDF file with step by step instructions. It also supposedly works if your laptop's internet is coming in via LAN cable.
But an interesting claim is that even if your laptop's source of internet is wifi, you can in turn re-broadcast the internet, turning your laptop into a repeater. So if laptop A is in range of the wifi router but another laptop B is out of range, but in range of laptop A, with mary-fi laptop A can repeat the wifi signal to laptop B. Pretty cool trick. Unfortunately I haven't tried it yet so I cant confirm because I need to borrow another laptop to do that.
As of now, the website of mary fi is down. This is what I can see
ForbiddenYou don't have permission to access / on this server.
Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.
Fortunately, I have mirror links to the file, that is an alternate download link.Filename is Maryfi-EN.exe (2.07 MB)