I tethered via my Sprint EVO on borderline 3G here for a few months. I was averaging about 1.2mbps over the 3G link, so nothing stellar, and my pings were around 170-220ish. Not great, but usable. I was able to do 5x clients, with the fairly rare glitches that would drop me offline. It seemed to be fine for most normal tasks, though things that normally lag everyone (Dalaran, large PVP fights like city invasions, etc.) were much more prone to problems. My mother tethers via Verizon 3G out in the boonies and aside from the occasional lag in big cities, she doesn't have any issues multiboxing 2 clients.