I've already tried all possible (http://ubuntuforums.org/showpost.php?p=10129571&postcount=43) solutions, no progress. I'm in despair. In Windows (on the same machine) this adapter works stably.

Device: Trendnet TEW-649UB.

System details: Ubuntu 11.10;

leventov@leventov-ubuntu:~$ uname -a
Linux leventov-ubuntu 3.0.0-12-generic #20-Ubuntu SMP Fri Oct 7 14:56:25 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux
leventov@leventov-ubuntu:~$ lsusb
...
Bus 002 Device 002: ID 0bda:8172 Realtek Semiconductor Corp. RTL8191S WLAN Adapter
...
leventov@leventov-ubuntu:~$ dmesg | grep 8712 #current driver
[    8.146510] r8712u: module is from the staging directory, the quality is unknown, you have been warned.
[    8.147113] r8712u: DriverVersion: v7_0.20100831
[    8.147124] r8712u: register rtl8712_netdev_ops to netdev_ops
[    8.147127] r8712u: USB_SPEED_HIGH with 4 endpoints
[    8.147478] r8712u: Boot from EFUSE: Autoload OK
[    8.551272] r8712u: CustomerID = 0x0000
[    8.551275] r8712u: MAC Address from efuse = 00:14:d1:6c:52:19
[    8.551625] usbcore: registered new interface driver r8712u
[    9.501351] r8712u: Loading firmware from "rtlwifi/rtl8712u.bin"
[   10.160471] r8712u: 1 RCR=0x153f00e
[   10.161241] r8712u: 2 RCR=0x553f00e
leventov@leventov-ubuntu:~$ lsmod | grep 8712
r8712u                189049  0 t