@hek : it happens that I have currently the same setup (3.3v mini pro as serial gw via FTDI); and am suffering from exactly the same symptoms (no reaction when I push commands to the GW). Reception, however, is ok. I plan to add a capacitor for the ripple; but given incoming reception is ok, I doubt it will make a difference?
Needless to say that uploading the sketch works fine, and that upon writing the TX led flimmers.
EDIT : nevermind, solved.