If File Sharing starts slowly on cold mornings, try deleting the AppleShare PDS file that lives at the root level on each shared volume. Jon Pugh <email@example.com> posted this tip on Info-Mac, saying that it took File Sharing about an hour to start up on his PowerBook, and after deleting the file, it took less than a minute. My Mac always seemed to start slowly as well, so I used ResEdit to make the AppleShare PDS files on all my volumes visible (at which point you can see the snazzy killer rabbit icon), trashed them, and then rebooted. I presume that File Sharing rebuilt them on the subsequent reboot, and File Sharing starts up much faster now. You will lose all your sharing preferences, but since I have nothing fancy set up, it wasn't a problem for me. (I just log in to my SE/30's volumes from the PowerBook as the owner, which allows me to avoid setting up sharing for each individual volume. I once heard that using the Finder's Sharing menu item to share the disks, which lets you share specific folders and set more specific privileges, exacts a small performance hit.)
Option-Click AirPort Menu for Network Details
If you hold down the Option key while clicking the AirPort menu in Mac OS X 10.5 Leopard, you'll see not just the names of nearby Wi-Fi networks, but additional details about the selected network. Details include the MAC address of the network, the channel used by the base station, the signal strength (a negative number; the closer to zero it is, the stronger the signal), and the transmit rate in megabits per second showing actual network throughput. If you hover the cursor over the name of a network to which you're not connected, a little yellow pop-up shows the signal strength and type of encryption.