After upgrading my Raspberry Pi Wheezy to the latest kernel 3.2.27+, my wireless adapter EW-7811Un stopped working.

Here's the fix:

su - root
mkdir ~/drivers
cd ~/drivers
wget http://dl.dropbox.com/u/80256631/8192cu-latest.tar.gz
tar zxvf 8192cu-latest.tar.gz
cd 8192cu-latest
install -p -m 644 8192cu.ko /lib/modules/3.2.27+/kernel/drivers/net/wireless
depmod -a
cat <<EOF >> /etc/modprobe.d/blacklist.conf
blacklist rtl8192cu
EOF
cat <<EOF >>  /etc/modules
8192cu
EOF
shutdown -r now

After reboot you should have wlan0. You may need to configure your wireless network if you didn't so already, by editing /etc/network/interface. Recommended that you use wpa_passphrase to generate your encrypted wifi password:

wpa_passphrase mywirelessnetwork_SSID

Then edit /etc/wpa_supplicant.conf, using the output of wpa_passphrase:

ctrl_interface=/var/run/wpa_supplicant
network={
    ssid="mywirelessnetwork_SSID"
    scan_ssid=1
    proto=RSN
    key_mgmt=WPA-PSK
    pairwise=CCMP
    group=CCMP
    psk=.......
}

And lastly:

cat <<EOF >> /etc/network/interfaces
iface wlan0 inet dhcp
pre-up wpa_supplicant -Dwext -i wlan0 -c /etc/wpa_supplicant.conf -B
EOF

Now enjoy the WiFi back on your Pi again.

Thanks to Wolf Paulus, who solved the problem with Kernel 3.2.27+ and provided links for the compiled binaries.