FWIW, on my newer 2.2Ghz i7-based MacBookPro, I can reproduce the problem but I see satisfactory results by setting the delay to just 10 rather than 100. So, it is likely that the minimum delay is system- and application- dependent.  Since there's not likely anything to be done here in Tkinter, I am going to close this issue.  Perhaps some day down the road, work being down now by Guido in PEP 3156 may provide a better way to integrate Python event loops with Tk's and Cocoa's.