Even with razieh's UI mod which is basically a visual of when autoattack goes off, it's only really worth it to time autoattack on bump -> nightstrike combo and be aware when casting thunderous overtune / painful lamentations. Ex. don't begin casting it when you see the bar 1/2 to 2/3 filling up.
With that said, it doesn't improve DPS by very much unless you have a 0 lag environment which for me isn't often. Even small delays (0.0 - 0.5 sec) are enough to fuck up the timing and negate the benefits from doing it.
I think people think they see a huge increase because of Confirmation bias theory.
http://en.wikipedia.org/wiki/Confirmation_bias