I had a Curve 9300 3G when I got my Playbook on release day, all functions worked flawlessly except the Bridge Browser where I received a "MDS Service Unavailable u427" message. I recently upgraded to a Bold 9780 3G again with Bell Canada and still the same problem. I connected to a buddy's Torch today (personal BB without a BES) and the bridge browser worked well which makes me think that the BES at my company is the problem. The web browser on the 9780 works well and it also tethers perfect but after a HUGE bill I don't do that anymore.
Use the other regular browser while bridged, not the bridge browser. The last update corrected the problem you are experiencing for me, as I had the same problem. See if that works.
