To keep your computer in top working shape, it is best to completely quit applications that you are not using, this means using the quit item from the application's menu, not just closing the window. The easy way to do that is pressing Command+Q
Another good one is to reboot your computer often, preferably at least once a week. Sleeping the computer by simply closing the lid does not have the same impact as a good old fashioned restart.
Quitting Microsoft Entourage nightly is a must, if you fail to do that, it will not clean out the junk folders, and it will not properly rebuild it's internal indexes of your email. The impact of not quitting nightly is Entourage taking up more memory, slowing down your other applications, and significantly slower searches of your emails.