I too had no issues with repeating keys and WoW ToS/GMs. I have two foot pedals each programmed to spam a key then when released press another key once (stop casting macro). So it looks like this when you hold it for awhile then release:

11111111112

Mind you there are no delays at all in the macro. It looks exactly as if you spammed the key by hand over and over about 4 presses a second.

I can use this as both my spam flash heal/attack castsequence macro or as stop casting since the key at the end is stop casting.

Ziran