When is it acceptable to use Internet abbreviations such as “u” or “r”?

In my business communication over Internet text messengers, for example Google Talk or Skype, I see that many people often use shorten words like u instead of you, r instead of are and the like.

How appropriate is usage of such words in contemporary communication? Is it used in emails also? Should we avoid it as much as possible?

I think the first thing to say about this is that it’s always acceptable to avoid these abbreviations... even in the shortest, most intimate SMS or instant message, a fully-spelled-out you or are would never be seen as too formal.

That being said, if you are worried in the least that the person who you are corresponding with might think you are stupid, uneducated, or inappropriately informal, then using “u” or “r” in communication will give them an easy reason to believe that you are.

I would say I personally never use them, but that would be a lie. Sometimes in very hastily composed text messages on my phone I will take such a shortcut. But if I have a full (real) keyboard at my disposal and no 255-character limit, then there's no excuse for such sloppiness.

On the other hand, if your correspondent is using them there’s no reason other than personal pride why you shouldn’t use them back to facilitate the conversation.

Personally I would avoid shortcuts like "u" or "r" in any business emails (and in personal ones too actually). Depending on the recipient, they might make you seem more adolescent or even, um, less smart than you actually are.

At best, such shortcuts have no effect on how the recipient perceives you or the message. But considering that you do not really save time or anything else using them (when you are composing an email with a real keyboard, that is), is it worth taking the risk?