I’m currently sitting in terminal 5 of the heathrow airport finishing a blueberry muffin while waiting for my corresponding flight back home once again, as I want to reconnect to the digital world, I am greeted with a 30-minute limit of free wifi. It seems like it is becoming a global trend in coffee shops and other public places nowadays. Anyways here is the procedure to circumvent such limits by spoofing your mac address:

On a mac/linux:
ifconfig to find the status: active network interface. On the latest pros and airs, it should be en0. Note the mac address somewhere to revert back once the operation is complete.

sudo ifconfig en0 ether [new_mac]
sudo ifconfig en0 down
sudo ifconfig en0 up

On a win7/win8:
Seems like microsoft forces you to use one of those mac addresses:

X2-XX-XX-XX-XX-XX
X6-XX-XX-XX-XX-XX
XA-XX-XX-XX-XX-XX
XE-XX-XX-XX-XX-XX

You can change mac address by simply using a program like http://lizardsystems.com/downloads/changemac_setup.exe