How Much is Too Much?

It isn't easy for a new author trying to make a name for herself or himself. There is a lot of competition out there for readers' hard-earned money. And now with self-publishing becoming so popular where anyone can upload a book, it's even harder for an author to make those much-desired sales.
Which leads me to the topic of promotion. Authors will try whatever it takes to get noticed. It might be ads, blogging, requesting reviews. They might hand out cute little trinkets at conventions, something to hopefully make you remember them the next time you go shopping for books.
And then there's Facebook and Twitter. I doubt if there are many authors who don't have at least one of these accounts. I have both, but don't post much. I'm a full-time author, which means I'm home in front of my computer the biggest majority of my time. That doesn't leave a lot of chances to do something exciting, something I think is worth sharing with the people who friend or follow me.
Because I don't look at Twitter every day, certain tweets will jump out at me when I do sign in to my account. I see tweets from some authors that say the same thing over and over. I have to admit seeing the same authors posting the same tweets about their books gets old. I'm so sick of seeing the titles of those books, there's no way I'd ever buy them. I doubt if that's the result the authors want to get with their promotion.
I've always heard a person needs to hear or read something at least six times before s/he remembers it. Do you believe that? Should an author keep pushing the same type of promo in the hopes of finding new readers? Or is that same promo driving away the readers s/he already has?
How much is too much?
Lynn