I've heard tell of WiFi troubles with Leopard but it hasn't really bitten me (or I haven't realized that it has) until now.
I'm working from home today and I've lost my VPN connection with work twice. Both times I had booted my Macbook into Windows and I was rebooting into Leopard. When the Macbook comes up in Leopard suddenly none of my computers can associate with my Linksys router until I cycle power on it. It is as if the initialization and hand shaking of my airport connection just whacks out the router. The problem with that theory is that once the router is rebooted and the Macbook associates, my Windows, work machine associates just fine as well. Perhaps the problem exists when my windows machine is the first to associate with the wireless router or has something to do with my VPN connection. I don't think that is the case. It just doesn't make sense. I'm grasping @ straws a bit here. I can't really test my theories right now because I have work to do and I can't afford to kill my VPN pipe.
Speaking of which, I better get back to it. I'll let you know if I figure anything out later.