Last summer I upgraded the network at Corp HQ to 802.11n. I decommisioned every 10/100 Ethernet switche and disconnected all ports. For the backbone of the new network, I installed new Gigabit Switches connected by fiber.
On each floor I connected Apple Airport Extreme Base Stations running 802.11n @ 5Ghz and an Apple 1GB Time Capsule. Each plugged into the Gigabit backbone.
Everyone in the company got either a MacBook, 15" MacBook Pro, or 24" iMac depending on their needs and our 7 year old Linux servers were replaced with 2 Apple Xserves. Every system connects to the 802.11n network. Network authentication is handled through RADIUS on the Xserve and encryption is handled by a Fortress Technology appliance with 256bit AES encryption. We replaced the 15/2 Business Cable connection with a 50/20 Business FIOS.
I've had no issues except stupid users, everyone is connecting at 300Mbps, and everyone loves the speediness of all the LAN services and the Internet.
I'm glad to be rid of the Ethernet.