I had problems with the wlan as well -- I could connect, but it lost connection every few minutes and I would have to manually disconnect and reconnect. The problem only occurred with the N protocol (b and g were fine). After a long time, I finally found the solution and it has been fine for several months:
1. Install the proprietary Broadcom STA driver from Additional Drivers
2. Enter terminal:
Add the following to the end of the file:
sudo gedit /etc/modprobe.d/blacklist-bcm43.conf
You might have to restart for the changes to take effect, but basically, the open source driver does not operate with N well at all. But, when you install the proprietary driver, the system will keep using the open source drivers unless you blacklist them. Once you blacklist them, it will use the Broadcom STA driver.
If you still have issues, try modifying your wireless settings and set the MTU size to 1500 & IPV6 to Ignore.
Hope that helps.