i'm in the middle of a 40 hour compressor transcode from FCP timeline for a 3 minute music video (see my post in the 'compositing' section if you would like to help me figure out why it is sooooo long...) and the screensaver won't kick in. any ideas why? it is set to start after 15 min. in system preferences... i am using the fullscreen iTunes visualizer in its absence.
i'm on a 10.5.3 MBP 2.6 ghz and 4gb RAM running FCP 6.0.1 and compressor 3.0.1.

First, to help keep the OS in the cleanest environment possible and to not take clock-cycles away from FCP or Compressor during encodes, the screensaver should be disabled. You don't want any automatic operations going on in the background that could potentially cause a hang during an encode or as I say, steal away resources from the most important and most CPU intensive task your computer is doing.

If you're concerned about long-term burn-in just manually turn the screen off. You'll be saving power and extending the life of the screen anyway.

Turn off screensaver, auto spin-down for HDD's and any other "automatic do-this" function in system preferences and help your system be more efficient.

Good points!
but is there a way to SAFELY turn off the MBP display in mid transcode aside from putting it to sleep? i fear that very much at hour 18 of the transcode!!!
i suppose in the future i could put it to sleep and THEN start the transcode with an external monitor hooked up (with a power button!)...

Look at your function keys; the F1 & F2 keys control screen brightness; just pull it all the way down and the backlight will be off, negating the need for any screensaver.

thank you, Robert.
the simplest things seem to escape me...

I have all our systems set to put the display to sleep after no use for 45 minutes. Never had any problems. Takes no additional CPU cycles and because it happens automatically, you don't have to worry about it. Here's my settings from System Preferences>Energy Saver.