Just to report it:
I am updating my system regulary with 'yum update'.
I also did that at end of March 2008 and after that 'successful' update I was not longer able to connect to my WPA2 protected WLAN at home.
(No changes at the WLAN\access point configuration at all).
I had to uninstall wlassistant and wpa_supplicant (1:05.10-4.fc8), to disable the update repository (to reinstall the original versions) und to reinstall wlassistant and wpa_supplicant (1:05.7-15.fc8) to have the WLAN connectivity work again.
Hardware: Fujirsu siemens laptop amilo Si1520
WLAN card: wla9 Intel PRO/Wireless 3945ABG