eHomeUpgrade talks to Atheros about its double-speed modes: Atheros's turbo modes (Super G and Super A/G) boost raw throughput on their equipment to 108 Mbps. Net throughput? Dunno. But it will be compatible among vendors choosing Atheros's gear, depending on local regulation factors.
Frame bursting, mentioned here in passing, should work across many vendors' equipments -- at least with ongoing firmware upgrades -- and should dramatically or at least relatively improve the net bandwidth of 802.11g networks and b/g networks by reducing the clutter of very short g packets.