For some reason, after installing Leopard onto my powerbook G4, the WiFi connection has become sporadic. I thought it was just the powerbook, but it's like that with my new iMac as well.
i am having the same problems. Two macbooks and an imac connecting to an airport extreme and an airport express are all sporadic post installation and seem to have decreased reception.
meanwhile my IBM laptop is experiencing no issues connecting so it appears leopard has some serious issues...
We've been experiencing this for almost 3 weeks now. I'm blaming that airport update around that time and will be reverting to the older airport update as soon as I can figure out how.