[citation][nom]1jadedattcustomer[/nom]To the uninitiated, to fully utilize your 5, 10, 20Mbps internet connection, a 54Mbps 802.11g is more than sufficient.[/citation]
To the uninitiated, wireless networking has very large overhead, around 30% even with a very good connection. If your connection is poor, you can easily lose the majority of your bandwidth to retransmits and other WiFi overhead. Long story short, your 54 Mbps router is not providing anywhere near 54 Mbps unless you are inches from the router, and even then you'll lose some bandwidth.
Multiple people sharing the network will further reduce your bandwidth, as will increasing your distance from the router, putting obstacles in the path and interference from other sources of 2.4 GHz radiation. Bandwidth overhead is sky high in most home wireless networks.
A decent 802.11n router is plenty for most applications, but 54 Mbps is not usually enough for smooth streaming of HD video over the internet. 802.11ac is of questionable value to people who already have an 802.11n network, though there are still great applications for it, like local streaming (rapidly rising in popularity with the proliferation of set top boxes), network attached storage and local file transfers.