This is a perfect application to mention before the weekend. Cortado has another free application called Save The Weekend which tries to do exactly that. It tries to create work free weekends and evenings by delaying every email you send outside of work hours until work hours commence. In other words if you have a great brainstorm at 2AM you can send it and your BlackBerry will actually send the email when work hours begin.
The cool part is that you get to decide with each email if it should be sent immediately or be delayed until work starts. You get to customize your own work hours and decide if it should also delay all weekend emails.
NOTE: The main downside of the free version is that it adds a footer at the end of the email that says it was sent by Save The Weekend
They also have a premium version for $6.98 that lets you remove the footer from your delayed emails. It will also allow you to set it so that emails you send on Friday are not sent until the next day or business day.