As I implied, if not stated outright, before; its usage is more appropriate to intimate personal written communications than published writing, (or the written word that is to be read by those that don't know the writer personally).
The only place for it in published writing is in dialogue, and only where it fits the character, for example when the character is a 'sloppy' speaker and drops the end letters of words.
To my mind it implies a miniscule shortening of the already single syllable word, coupled with a diminished meaning to the word 'love' - if that makes sense.
Use it in written conversation, by all means, but the difference is generally too subtle to bother with. If in doubt, use 'love'. Few, if any, people will say that 'luv' would have been better, though there will always be some that get their heads up their arses about 'luv' being used at all..... let alone being used inappropriately.
This thread has been interesting.... it's made me think about something that I'd just not really noticed before.... just accepted.
I did a word search on my 150,000 word novel to see if I'd used it in any of the dialogue and it wasn't found.... though I had used 'luvvies' in a conversation where a character was referring to partygoers from the theatrical profession - It's a term that's in common use here in the UK.