From The Guardian:
There are lots of people these days with figurative underpants on their heads. That's because in the internet age, the exclamation mark is having a renaissance. In a recent book, Send: The Essential guide to Email for Office and Home, David Shipley and Will Schwalbe make a defence of exclamation marks. They write, for instance, "'I'll see you at the conference' is a simple statement of fact. 'I'll see you at the conference!' lets your fellow conferee know that you're excited and pleased about the event ... 'Thanks!!!!'", they contend, "is way friendlier than 'Thanks'."