Here's an idea for Microsoft's Visual Studio.Net Editor team, or for the guys doing SharpDevelop or other IDEs...
What about having a code editor with code visibility modes? For example, Full Mode, Debug Mode and Release Mode.
When editing in Debug mode, stuff like Debug.Assert statements and #if DEBUG... #endif code would be visible; when editing in Release mode, they would not (but #if RELEASE...#endif etc. would). When editing in Full Mode, everything would be visible.
This way, developers can switch off display of Debug stuff when they really need to focus on algorithms and other implementation details, without being bothered by ugly-looking Debug code.
What do you think?