1. FreeBSD 6.2
And Paste. The most interesting thing I saw was the bug that caused it found right at the bottom:
"... unindent does not match any outer indentation level (account.py, line 68) ..."
While it's easy to config your own editor . There are other factors
* uncommonly used editors 
* other users/developers
Of the two, other developers is the biggest pain. You have to make sure each developers editor conforms to your coding standards.  But making "quick changes" on the server, can short-cut such safeguards.
ruby -c foo.rb
Only problem is, the guy edited the code directly on the live server without testing.