As a programmer myself, there is no reason for undo to impact performance, unless too many bits change to hold both versions in memory. Deleting a character should only change one pointer in memory. Applying a Photoshop filter to every pixel of a 2000x2000 image is another story ... However, re-arranging application code that didn't do undo right in the first place is a substantial effort that could introduce more bugs. I suspect they simply couldn't afford the time and the risk. Regardless of the reason, the end result is sad. I am hoping Poser 5 will attract a larger user base. Poser 5 has such cool new features. Now, if Curious Labs can just "get the basics right". For me that's: (undo; stability; being more responsive when user clicks cancel in the middle of a lengthy calculation). Any why are the parameter dials now part of a fat pop-up window that is constantly in my way? In Poser 4, I put the dials under the library pull-out to save screen space. No can do in Poser 5.