The exclamation point expresses a strong degree of surprise, incredulity or other emotion:

• Boo!
• Holy cow! That is one large ball of twine.
• Schnikies — that was a fun party!
• I’m gonna wash that man right outa my hair!
• Sunshine on my shoulders makes me happy! (OK, so it doesn’t work so well here, but check this out.)
• I won the flippin’ lotto!!! (If this is the case, and you happen to be writing out the statement, by all means, feel free to use more than one exclamation point to get your enthusiasm across. For most cases, however, one will suffice.)

Placement with quotation marks
The exclamation point goes inside the quoted material when it refers to that material: “We’re having smashed potatoes and cheese wheels for dinner and you’re gonna like it!” he exclaimed.

It goes outside the quotation marks when it doesn’t refer to that material: I love reading “The Scarlet Pimpernel”!

Other punctuation
The exclamation point stands alone when it comes to ending sentences. Do not add a comma or period after an exclamation point. No matter what.

Placement in advertising
Don’t do it. Much like the sunburst in lame advertisements, it cheapens your product.

Usage: single vs. multiple
If you’ve ever received an e-mail from me, you’ll know that I use this punctuation mark almost as often as I inhale. It’s a habit I’m trying to break, but I’ve at least kept it out of any kind of serious writing (i.e., what I do for a living). People must have outlets, I say, so exclam away in your e-mails — if it doesn’t offend too many people. Just make sure to limit your !!! to the most casual of instances.

Happy trails!

SAK