Tonya and I were watching The Simpsons (not a habit, but see "The Simpsons Takes Aim at Apple", 2008-12-02) on my MacBook via Hulu the other night, only to be interrupted by the screensaver kicking in every 5 minutes. I could have disabled the screensaver, of course, but I didn't want to stop the program, so I just kept touching the trackpad every few minutes. How stupid is that?
That's why I was happy to learn about a free application that solves this problem elegantly. Lighthead Software's Caffeine puts a tiny coffee cup in your menu bar. Click it and your Mac won't go to sleep, dim its screen, or start the screensaver, no matter how you have configured the Energy Saver and Desktop & Screen Saver preference panes. (Another click turns Caffeine off again.) Command-click the coffee cup to display a menu that lets you access preferences and set a duration for Caffeine to work its magic (if only that was available for real coffee!). The simple preference window lets you add Caffeine to your login items, display the preferences on startup, and set a default duration. The duration setting is particularly appreciated, since you don't want to drain your battery unnecessarily just because you forgot to disable Caffeine.
My suspicion is that most Macintosh-based video-playing applications already do exactly what Caffeine does, whereas Web-based media players can't access system-level settings like sleep and screen dimming. Caffeine will be welcome for anyone using services like Hulu, Joost, and Netflix's Watch Instantly feature for Intel-based Macs (see "Netflix Starts Deploying Mac-Compatible Media Player", 2008-11-03). (Note that those services are available only for people accessing the Internet from within the United States; a small amount of payback comes from the BBC, whose iPlayer will play video only within the UK.)