One interesting thing is if you use it verbally, your tone and maybe body language will convey more on what you want 'dear' to mean. But if one would send a text message like chat or sms to a casual acquaintance of the opposite sex messages such as 'Good morning dear' or 'Are you busy dear?', could it be misleading?
I hope I'm not being too old fashion or something, but I think there can be some differences and or misleading element if the word 'dear' is used on casual friends.
However, I do think that, with additional one word would greatly reduce that effect. That's the word 'my'. For example, I do think it's ok that, while in a conversation with a causal friend like 'I think you are right my dear'. I do think when used in such context, it's quite ok and more widely acceptable. But if you say 'I think you are right dear' or 'Dear, I think you are right' then it can be quite misleading to some great extend.
I know that in western culture, this can be quite common to call someone dear or honey, but I think we Asian still have not reach this stage yet. For most modern Asian, the word 'dear' or 'honey' still pretty much used mainly toward our loved one, ie our partner, lover or spouse.
For myself, I only used the word 'dear' on my girlfriend who are in a relationship with me, but when I speaks with my friends, especially those few close female friends, I would use the words 'my dear', some times, not all the time neither it's that often. I do think this will help to save me many unnecessary misunderstanding, headaches or even unnecessary quarrels.
What about 'Dearie'?
Speaking from experience, I used to have acquaintances addressing me using 'Dearie'. And frankly speaking, it felt kinda funny to me.
But Newman, I agree with one of your post - the tone and the body language does matter too.
I don't have problem people calling me dearie or dear or darling or anything.
To me, if your heart is pure and true to your love ones, whatever my friends call me is ok with me as long as they find it comfortable.
There is always a line which one draws but so far I have never ever encounter any problems. Maybe I have understanding friends who are open minded (Most of them are young Asians executives).