If you have an iPad, you may have run into odd little WiFi related problems. I know I have. MacRumors mentioned a couple of workarounds including updating WiFi Router firmware, using WPA/WPA2 (this was puzzling at first), adjusting screen brightness (even more puzzling), and renewing the IP address.
I found two Apple Support knowledge base articles related to iPad WiFi problems:
The second support article has the most information though several suggested workarounds are puzzling. Some are understandable. The suggestion to use WPA/WPA2 encryption instead of WEP has nothing to do with fixing the problem. It is just a way to get around having to retype WEP keys after a disconnection. Adjusting screen brightness higher and turning off the auto-brightness setting is still puzzling. Apple offers no explanation why this might help with WiFi connectivity issues.