[axelav]

if you're on a mac, Gas Mask is a really good tool to switch between different /etc/hosts files

http://www.clockwise.ee/gasmask/

here's my 'focus mode'

https://gist.github.com/2564478

[M4v3R]

Also, try Self Control app: http://selfcontrolapp.com It has a black/white list (depending on what you need) of hosts, and lets you set up a timer.

[cstuder]

On Windows, there's Focal Filter which changes the hosts file for a given period of time.

http://www.focalfilter.com/