To paraphrase John Lennon:
Sweet Rosetta fat she thought she was a cleaner, but she was a frying pan.
When Apple made the switch from PowerPC chips to Intel chips several years ago they had the solve a daunting problem: PowerPC code doesn’t run on Intel chips. They devised an ingenious emulator called Rosetta to work behind the scenes and translate everything on the fly. Running PowerPC code on your Intel Mac is a touch slower because of this emulation layer, but it sure beats not running it at all.
Unfortunately, Snow Leopard (Mac OS X 10.6) not only dropped Rosetta as a default install, it also introduced a horrific bug, still present as of 10.6.1. With the bug, text input into a PowerPC application causes Rosetta to barf hard, resulting in a brief blue-screen followed by the log in window. In other words, your account gets totally taken down along with all applications you running. Documents or files which were open but unsaved are lost.
This is, quite frankly, the worst Mac OS X bug I’ve seen in years, and one of the reasons I always recommend that people wait for the “.2” release of any Mac OS X upgrade—in this case, Mac OS X 10.6.2. For those who’ve already upgraded or who purchased a new Mac with Snow Leopard already installed, stay away from PowerPC applications requiring text input until this gets fixed. (You can do a Get Info on files to see if they are PowerPC or not.)