Remember: The best rule of thumb is to communicate with proper grammar whenever possible. Yes, there are unique circumstances where Internet shorthand is acceptable (like tweeting), but overall your communication style reflects on your professionalism. People tend to remember the little things, bad grammar included.
This is a good article about business communication. As employees become more used to internet shortcuts used in texting, tweeting, and other informal communications, it becomes crucial to show professionalism by writing in plain English.
One important item that the author does not mention is to spell out a technical term instead of using an acronym, at least the first time you introduce the term into a conversation. You should not assume that everyone knows or remembers what the acronym stands for. People will not usually ask for clarification in fear of seeming ignorant. It doesn't take many more characters or syllables to spell out the whole term, at least once, and this can go a long way towards more effective communication. Technology does not have to be a club with a secret handshake. Spell it out, and make more sense!
Here is my famous Tweet on the subject:
I find it a worthwhile challenge to see how well I can write a "tweet," full of content and meaning, without having to resort to "IM speak."