I am using Shake 4.1 on a macbook with 2GB RAM from Samsung.
Mine did not have any such problem until I upgraded to OS 10.4.9
It could have also been an upgrade prior to it since I had not been using Shake on my macbook for a while.
I get strange super-italic font in text boxes with reddish, glitchy selection highlights and the system freezes (unable to force quit) at certain drag and drop attempts from Finder (this had never been a problem before).
I suspect it to have something to do with the new fixes to Finder's media file handling. It now works fine with Apple's current inhouse software like Aperture and iMovie but it gets cranky with Shake.
For your information, my macbook also have international keyboard layout for Japanese and Thai enabled . . . but that had never been a problem before though. The OS itself has conflict with certain localized font and the problem is simliar to what observed in Shake. But I am not using any such fonts in Shake.
I know my macbook is not the right platform for Shake nor any real compositing, I bought the copy mainly so I could continue script coding at home. It works mighty fine with an external monitor though.