Been using Stanza Desktop regularly lately as I'm traveling and eBooks make much more sense than heavy volumes. I'm particularly fond of the auto-scrolling feature included in Desktop as opposed to the iPhone version (not sure if it would work there?). One problem, however, is that on my MacBook Pro the screen is set to dim after 5 minutes and go to screensaver after 10 - while many programs include mouse/keyboard activity to stop this, Stanza Desktop does not and for some reason exclude a "Disable Screensaver/Dimming when reading in fullscreen" option as is found in most video players (i.e. QuickTime or iTunes). I hope this functionality is included in the future.
Alternative
I know this is an old post, but I just tripped over it searching for something else -- try grabbing a copy of the Mac menu bar app "Caffeine"; it's free and it'll prevent your screen dimming/blanking at a single click. You can either toggle it on/off manually, or set it to disable the screen sleep for a set number of minutes (so you don't forget to turn it off.) Maybe not as nice as having it built into the app, but it's helped me out with a lot of different apps that all suffer from the screen blanking problem. And like I say, it's free...