For those who have trouble staying on task for hours at a time. Which probably means most computer users. Several applications now exist to block off Internet access, selectively block programs, etc. I do this by not turning on my wireless – but then I can’t stream music. So I’ll try something more elaborate.
Economist article: Software that disables bits of your computer to make you more productive sounds daft, but may help keep distractions at bay
Freeware: SelfControl 1.2.2 Block distracting websites for predetermined periods of time SelfControl is an OS X application which blocks access to incoming and/or outgoing mail servers and websites for a predetermined period of time. For example, you could block access to your email, facebook, and twitter for 90 minutes, but still have access to the rest of the web.
Art and Science in Technology - Roger Bohn's Blog 