Option-clicking on certain icons on the right side of the menu bar provides additional technical information.
As noted in this hint, for example, you can easily see more detailed Bluetooth information. What's new in 10.5, though, is detailed information in the AirPort menu item. Clicking on the AirPort signal icon in the menu bar normally shows only the network name and whether it's secure or not.
By Option-clicking, you can also see the AirPort's MAC address, channel, signal strength (RSSI), and transmit rate, as seen in the image at right. With this new feature, the AirPort signal menu bar icon is useful when setting up or troubleshooting a wireless connection.

