802.11g runs on the same band as 802.11b so a g device such as a laptop will communicate just fine with b hotspots. One thing to remember is that the speed of a connection is not just about the speed of the card. On public networks, you'll never be viewing ESPN at "g" speed because you're limited by the speed of the internet connection (about 1/5th the speed) along with the others who are sharing that connection.

The real advantage is sharing files between computers on the same network, say in your home or office, where data can move at 54 megs between these "local" machines, even though the outside connection speed to the Internet is limited by your DSL, cable modem or 10baseT network. Another thing to keep in mind is that the slowest client will bring down the speed of the WiFi network. This means if one client (PDA or notebook) is running 802.11b, an 802.11g access point will slow down to 802.11b speeds.