We've featured a few ways to keep distractions at bay when you need to buckle down, but The Apple Blog reminds us that you can block applications, sites and track time with the built-in Parental Controls.
If you need a bit of extra control when you're trying to work, you can use Snow Leopard's Parental Controls to block (or allow) specific applications, websites and even mail and messaging contacts to keep you on track. Plus, while it may not have all the features of your favourite time tracking applications, you can track how much time you've spent on each task through the logs it puts out. Hit the link for a more detailed walkthrough of the Parental Controls and how you can use them for yourself.
How-To: Turn Mac Parental Controls Into Productivity Boosters [The Apple Blog]