We've noticed this a bit ourselves, but reader ggperez points out that there's been some reports of Airport Wi-Fi dropouts on Mac laptops running Leopard. He describes the situation:
After a few seconds of internet browsing, the browser hangs up and you get a problem loading page/lost connection message (both firefox and safari). The problem is, Airport is still connected to the network. If you click the airport icon at the top of the screen airport status changes from "Airport Scanning" to "Airport on", then the internet works again. Only to go back into scan mode a few seconds later and repeat the cycle. There are MULTIPLE discussions on apples support forums, but no solutions.
A sample discussion thread can be found here. We wouldn't point this out if we haven't experienced it ourselves—both at home and at the luxurious hobo-stained Imperial Palace we stayed at during CES. Have you noticed this? We'd notice that one machine using Leopard would drop out while another one on Tiger sitting 2 feet away would stay up. You? Throw up a comment.