I have been using 3 usb data modem for the last four months.
Initially in August, the service was terrible with DL speeds in the 200-300K and upload less than 20k, conncetions unstable, snmp email not working, vpns not working.
Since August, matters have improved. I would decribe the connections I now get as stable most of the time (say 90%). The upload speed is ok now, in the 800-900k during off peak and 400-500 in peak times.
snmp email still is not working for me (my setup) but does work for some other email providers.
vpns still not supported, so connection to a corporate network will not work.
As mentioned above, try it for 14days, if you're not happy make sure you return within the 14 day period.
its also cheap --- the ryanair of broadband !