When learning IDL many years ago, the first thing that caused me to do a double take was the comma between a procedure name and its first argument when calling it and between either a function or procedure name and its first argument when declaring it. While removing this comma would not provide any noteworthy capability to my code, it would:

1. be one less keystroke per procedure call
2. eliminate approximately 25% of my syntax errors when writing in other languages
3. look a lot prettier
4. eliminate most of the shame I feel when showing non-IDL programmers my IDL code

If . can be used for the -> operator, the extra comma can be removed from IDL!