Hints reader nathanator11 discovered that Lion includes a handy app that provides all sorts of diagnostic information surrounding your wireless network. Much of the information the software generates gets pretty technical, but even Wi-Fi novices may find some of the details that the utility aggregates useful.
Wi-Fi Diagnostics is tucked away in the /System/Library/CoreServices folder. To get there, I pressed Shift-Command-G in the Finder (the equivalent of going to the Go menu and choosing Go to Folder), and then typed in the /System/Library/CoreServices path and pressed Return. Once in the folder, I found Wi-Fi Diagnostics and double-clicked it. Alternatively, you could launch the Terminal and type open "/System/Library/CoreServices/Wi-Fi Diagnostics.app", and then press Return.
However you find and launch it, Wi-Fi Diagnostics gives you four options: Monitor Performance (which shows you signal strength, noise level, transmit power, and data rate); Record Events (which can keep a log of network happenings); Capture Raw Frames (which records everything coming and going on your Mac’s wireless connection); and Turn on Debug Logs.
If you’re at all interested in what’s going on with your Mac’s Wi-Fi connection or your wireless network, Wi-Fi Diagnostics is freely included with your copy of Lion, and you can’t break anything by poking around the app—so enjoy!