I've been using my n52 with a repeat while pressed macro for 2+ years. I don't think it's legal in the strictest sense of the WoW terms of service, however Blizzard doesn't seem to care (which I'm not suprised about). My first button just spams the 1 key like no tomorrow when I play my rogue, but then again 90% of rogues do that manually, so who's the wiser?

However, getting more in depth with long delays and several different keys in macros is a different end of the spectrum. I personally wouldn't try it, even to make an autobuff macro.