Seriously.

Interjections are probably the most expressive part of speech. They are definitely the most disregarded and always have been... The main reason for the grammarians' neglect is that interjections operate outside of grammar—they are words that unilaterally express a sentence (or more) worth of meaning.... The Internet, where writing and talking sometimes seem to merge, is changing all of this.... It's not that e-mail, blogs, IM-ing, message boards, and texting have spawned a litter of brand-new interjections. (I don't count emoticons because you can't utter them, and I don't count acronyms like LOL and CU because they represent phrases with grammatical standing.) Rather, they have given lots of marginal ones, like awwa, a spelled-out form and thus a major shot in the arm.