I've noticed on more than a few occasions that some young people have begun to substitute the word prolly for probably. There are of course many examples of words that have been shortened to save on the number of characters required to send a text message but this one really bugs me. It only saves 2 characters so you gain very little but you lose a lot.
The word probably rests on mathematical and statistical underpinnings. It signifies that something has a better than 50% chance of being the case. So by using it and knowing the root of the word one displays an understanding of certain concepts of not only mathematics but also of logic and epistemology. By using probably one doesn't commit to a certainty, one claims that given the facts at hand the statement is not certain but only likely. By using prolly it only implies a vague likeliness not based on any rigorous consideration. It could be based on such nebulous folk concepts as intuition (see Malcolm Gladwell).
I'm convinced that some kids think that prolly is the proper spelling of the word and are already alienated from it's basis in inductive reasoning. I know that words alter in spelling and occasionally lose their original meaning. Terrific originally meant terrifying but hardly anyone today associates the word terror with terrific. Likewise, prolly is probably on it's way to becoming one of those words which will one day in the future be brought out by a stickler like me and shown to have had a much richer past than it would have been assumed.