I agree with Orange about the context in which words such as "love" are used. I find it a bit irritating if a much younger person addresses me in that way, but I wouldn't get up in arms about it. (I really don't like being called "dear" by anyone - and yet two of my friends use that term to each other as well as to me so nothing is meant by it).
I think why people get annoyed about it is that it could be perceived to confer a degree of power on the person saying it over the recipient. After all, it is unlikely that such informality would be used by a person towards his or her boss.
However, I think that many people who routinely use words like "love", "sweetheart" and "darling" are just being friendly. Generally speaking, this sort of thing doesn't bother me but, as with most things, context is important.