It goes without saying that more than one punctuation mark at the end of a sentence is one too many, no matter how strong a sentiment you're trying to get across. Oh, I've slipped up on occasion; it's laziness, really. I don't want to put the effort into using words that show I'm emphatic, so I'll slather my sentence with cheap punctuation and hope no one notices. One exclamation mark will do, thank you. Any more, and you're just using superfluous punctuation to compensate for lack of willingness or ability to state a position effectively.
But it's not just glaring punctuation violations that bug me. In e-mails where I work, everybody says "thanks!" when we mean "thanks." This isn't illegal or improper or anything, but it's dangerous. Generally, when I'm sending a "Thanks!" message, I'm thanking someone for telling me how to update a router firmware, and while I do appreciate this sort of information, it's not worth breaking out the pompoms, unless you're really into firmware (*cough*that's what she said*cough*). But if you don't conform to the punctuation expectation, you might seem ungrateful or sarcastic. I mean, you could say "Thanks. :)," but I think that's probably worse.
The real problem to all of this is, what do you do if you are emphatic about your gratitude? If you send me a box of chocolates, that's way better than information about router firmware. How do you express that? You'd have to say "Thanks!!" which, as I mention above, is a grammar felony. It's inflation, is what it is. Pretty soon we'll be taking a basket of punctuation to the market and having our baskets stolen, punctuation strewn all over the ground.
Who is to blame for punctuation inflation? I have a hypothesis, but it's one that makes me very sad. I think it may be comic books. Now I call it a hypothesis because, while comic books have committed horrific crimes against punctuation for many years, I'm not sure if those crimes found their way to the mainstream. Seriously, though? Marvel Comics seemed to have issued a ban on ending sentences with periods that lasted through the sixties and the seventies. And I don't mean that hyperbolically. I didn't have a lot of friends when I was a kid, apparently, because once, I counted all the exclamation marks in X-Men Issue 1. 551. It's almost as sad that I did that as it is that I still remember it. I've got a mouldering X-Men comic from the 70s in which there is not one single period. Heaping helpings of hyphens, dashes, and ellipses, though. To go with the roughly 20 exclamation marks a page. Yeah, I counted. Shut up.
That's all I got to say. Excelsior, ya'll!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!