I've posted an observation about this here that contains some tests about the CPU usage of the ActionScript editor in Flash 10.0.2. The problem is that the editor is slower than any editor I have used, including NetBeans which has the most active code coloring and code hints I have seen. And also, it's five times slower in Vista/7 compared to XP even when Aero is turned off. And I also have turned off all code hints and code coloring. Writing a quote letter (" or ') is especially slow and require a whopping 2Ghz (i.e. takes one second on my PC) in Vista, in a large .as file (500 rows or more), according to my estimates.
No other editor I have used (for example Visual Studio, DreamWeaver 8, TextPad or NetBeans) has ever come close to those numbers. Also, if all code hints and code colorings are turned off it should be as fast as Notepad, even for the quote letters which cause no coloring or other change in the document then. So it should take perhaps 2Mhz to write a quote letter, not 2Ghz.