I am using a Model B 256MB Pi with an Edimax EW-7711UTn USB WiFi adaptor. After some hours, the WiFi connection begins to drop and be restarted. Until it stops working completely. This is what I see in /var/log/messages:

Mar  9 20:39:29 raspberrypi kernel: [ 9353.773167] cfg80211: Calling CRDA to update world regulatory domain
Mar  9 20:39:29 raspberrypi wpa_action: WPA_IFACE=wlan0 WPA_ACTION=DISCONNECTED
Mar  9 20:39:29 raspberrypi wpa_action: WPA_ID=0 WPA_ID_STR= WPA_CTRL_DIR=/var/run/wpa_supplicant
Mar  9 20:39:29 raspberrypi wpa_action: ifdown wlan0
Mar  9 20:39:30 raspberrypi wpa_action: removing sendsigs omission pidfile: /run/sendsigs.omit.d/wpasupplicant.wpa_supplicant.wlan0.pid
Mar  9 20:39:33 raspberrypi kernel: [ 9357.478605] wlan0: authenticate with 30:46:9a:54:6f:3d
Mar  9 20:39:33 raspberrypi kernel: [ 9357.624628] wlan0: send auth to xxx (try 1/3)
Mar  9 20:39:33 raspberrypi kernel: [ 9357.626510] wlan0: authenticated
Mar  9 20:39:33 raspberrypi kernel: [ 9357.703189] wlan0: associate with xxx (try 1/3)
Mar  9 20:39:33 raspberrypi kernel: [ 9357.707045] wlan0: RX AssocResp from 30:46:9a:54:6f:3d (capab=0x411 status=0 aid=2)
Mar  9 20:39:33 raspberrypi kernel: [ 9357.722534] wlan0: associated
Mar  9 20:39:33 raspberrypi wpa_action: WPA_IFACE=wlan0 WPA_ACTION=CONNECTED
Mar  9 20:39:33 raspberrypi wpa_action: WPA_ID=0 WPA_ID_STR= WPA_CTRL_DIR=/var/run/wpa_supplicant
Mar  9 20:39:33 raspberrypi wpa_action: ifup wlan0=default
Mar  9 20:39:40 raspberrypi wpa_action: creating sendsigs omission pidfile: /run/sendsigs.omit.d/wpasupplicant.wpa_supplicant.wlan0.pid
Mar  9 20:39:40 raspberrypi wpa_action: bssid=xxx
Mar  9 20:39:40 raspberrypi wpa_action: ssid=xxx
Mar  9 20:39:40 raspberrypi wpa_action: id=0
Mar  9 20:39:40 raspberrypi wpa_action: mode=station
Mar  9 20:39:40 raspberrypi wpa_action: pairwise_cipher=CCMP
Mar  9 20:39:40 raspberrypi wpa_action: group_cipher=CCMP
Mar  9 20:39:40 raspberrypi wpa_action: key_mgmt=WPA2-PSK
Mar  9 20:39:40 raspberrypi wpa_action: wpa_state=COMPLETED
Mar  9 20:39:40 raspberrypi wpa_action: ip_address=xxx
Mar  9 20:39:40 raspberrypi wpa_action: address=xxx

And dmesg sometimes tells me:

[20014.112395] wlan0: deauthenticating from xxx by local choice (reason=3)

wpa processes running are:

 1872 ?        Ss     0:00 /sbin/wpa_supplicant -s -B -P /var/run/wpa_supplicant.wlan0.pid -i wlan0 -W -D nl80211,wext -c /etc/wpa_supplicant/wpa_supplicant.conf
 2010 ?        Ss     0:00 /sbin/wpa_cli -B -P /var/run/wpa_action.wlan0.pid -i wlan0 -p /var/run/wpa_supplicant -a /sbin/wpa_action

Does anyone else have these problems, and how can I fix those?