Using "dear", "darling", or "honey" to address a friend
Solution 1:
This varies greatly by geography.
In the Southeastern United States, it is not uncommon for some women to address or answer people--even strangers--of either sex with terms of endearment, such as Honey, Sugar, Sweetie, Darling, Baby, etc.
This practice is so intimately associated with "The South," that it will almost always be awkward or at best unusual for someone without a "southern accent" to speak in this way.
These terms do seem to be acceptable throughout the U.S. and Canada when speaking to a significant other or to very young children.
If this is not the way that you are known to speak, it could be awkward to use any of these terms to address a friend. It does depend upon the genders of speaker and the addressee, and the cultural/geographical/linguistic background of the addressee.
Solution 2:
I agree with Jay's answer, but would add that "Dear Sir", "Dear Mr. Smith", etc. used to be (still are?) considered standard openings for formal or business letters. In this pro forma context, the word "dear" is nearly meaningless. Perhaps at most, it means "I respect you, and I respect the tradition of opening my letter this way".
Solution 3:
Taking the geographical oddities a little further in Cornwall (South West of the UK) complete strangers, normally women, may finish questions with the term 'my lover'. IE "That'll be seven sixty my luuver" best pronounced with a distinct country burr.
Here in Australia there's an equivalent which is 'Darl' - short for darling, again best pronounced with a good Queensland aussie accent.
In answer to your question many couples have pet names, which are normally toe curlingly cute - fluff bunny, didums etc, but the use of darling, honey etc sounds a little 1950's to my English/Australian ear. We use mate a lot, as in 'Cheers mate' for anyone we're interacting with - works for friends and aquaintances - but then Australia is known for being very informal.
Solution 4:
In the American South, it’s quite common for women to address total strangers, as honey, sugar, baby, etc. (On TV, black men do too, but I haven’t observed this first-hand. It might be fiction.) It’s a tricky thing because you’re taking a very familiar attitude. If you’re a vigorous Southern woman with heaps of personality, it’s charming. You’re just irrepressibly friendly. For maximum effect, you have to give the impression that if the president of France walked in the diner door, you’d call him honey too.
But if you have to ask, don’t call people honey. Most people don’t, and you especially shouldn’t. You weren’t born into it. You’ll stand out.
In fact, if your demeanor towards someone is otherwise professional, and especially if you are a man and that person is a woman, never address them using such terms. It’s patronizing and offensive, an echo of the sexual attitudes of the 1950s and ’60s.
Solution 5:
In Australia and New Zealand you'll hear any of the terms luv, mate, cuz, bro, darl, darlin, honey, sweets, cobber, dear, sir, ma'am and even on occasion buddy, you guys, jokers, blokes, sheilas, and so on. It seems to depend on the individual as to when and how these terms are applied.
None of them are generally considered sexist or offensive when used casually but that too depends on the context because they can equally be used as terms of endearment or sarcastically.
At any rate, using any of the above terms to address another individual seems better than “hey you” and other less appropriate or derogatory terms such as babe, retard, wanker, asshole, and much worse. However, even these horrid terms are used quasi-endearingly within groups of individuals, especially teens.