Looks promising. But the performance with large bboxes isn't there yet.
Harry Wood's example works for me, I can also download banks in a 0.2x0.2 bbox, but trying to get banks for the whole of the Netherlands does not work yet. I get a "504 Gateway Time-out" message.
My test URL: http://openstreetmap.us/xapi/api/0.6/*[amenity=bank][bbox=2.5,50.7,7.2,53.6]