My brothers / SIL are Aunty first name / Uncle first name but I dont really like the concept of calling friends Aunty / Uncle - to me that's an endearment / sign of respect for family. I still cant bring myself to refer to SIL's fiance as Uncle (I'm not fully convinced they will get married I guess).
Older family friends / neighbours are Mr / Mrs Last Name, unless they come back and say they'd rather first names.
Good friends of our age we just use their first name.
The look on DS's face (20mths) when we try to explain that Rebecca is Reuben's (his best friend) Mummy was really cute, it was like he couldnt fathom there being more than one Mummy (me) in the whole world