A user running Mac OS X 10.6.8 was complaining of slowness when using Find in our editor. I reproduced the problem in 10.6.8 but not in 10.7 or newer. The problem is so bad that you sometimes have to reboot the computer because it'll just hang.
I tracked it down to our use of SCI_FINDINDICATORFLASH to animate the found text.
To make sure it wasn't a bug in my code, I rebuilt ScintillaTest with the project deployment setting set to 10.6 and ran it on a Mac with Mac OS X 10.6.8. I then pasted into the editor some code of a few thousand lines. I moved to the top of the file and yanked the vertical scrollbar down to the end of the file. Everything was fine. I then typed some text in the search field that I knew to be in the file. I grabbed the scrollbar and yanked it down again and then got the beach ball. If I don't force-quit ScintillaTest fast enough, my Mac essentially hangs. If instead of grabbing the scrollbar I just press enter while in the search field to jump to the next found search item, I'll see a enough lag in the animation where there can be multiple find indicators being animated if I keep pressing enter fast enough (this lag effect does not happen in later versions of OS X). However, all it takes is one occurrence of the find indicator to cause the problem.
As a workaround, I just don't use SCI_FINDINDICATORFLASH when my application is run on 10.6.