I myself have no issues. The foll. worked for me:
Try making a new network location and prioritzing network ports (airport should be first):
http://docs.info.apple.com/article.html?artnum=106653
Prioritize your preferred networks:
http://docs.info.apple.com/article.html?artnum=304482
Understand WPA encryption terminology and synch your Mac with your router, e.g.
WPA PSK (TKIP) = WPA
WPA PSK (AES) = WPA2
Probe for other nearby wireless networks to indentify their broadcast channels and avoid said channels for your wireless router.
Enable wireless g only on your router if all computers on your network have wireless g adapter cards.
hope this helps - good luck