I grew up in Texas, and referred to and addressed all of my aunts and uncles by titles when I was a child (as did all my cousins). Now that I am an adult, I might sometimes refer to my aunts and uncles with just a first name, but I can't even remotely begin to bring myself to address them without the title. I don't really know if they would have an opinion on what I call them (now that I'm nearly 30), but I can't do it. It's just too weird.
My brother and I and several of our cousins are married, and I don't think any of our spouses use the "aunt" and "uncle" titles. I think the spouses in general call their in-laws by their first names, or studiously call them nothing at all.
My husband's family, on the other hand, mostly lives in a country where not using titles would be unthinkable. So I call all of my in-laws with some sort of title, except for the ones who are younger than me (who instead use a title of some sort for me). The titles in use are basically the equivalent of "aunt" and "uncle" for people in your parents' generation or older, and "older sister" or "older brother" for people who aren't quite old enough to merit the aunt or uncle title, but are still older than you. They're usually tacked on to a person's first name or nickname, except within immediate families (i.e. my husband talking to his older sister) where it would be immediately self-evident who is being addressed/talked about.
With my own nieces and nephews, my brother's kids are kind of spotty about calling us aunt and uncle. He mostly calls me "Aunt Dindrane" when he talks about me to them, but they don't always use the title. Then again, they are also 1 and a half and 3, so I'm not about to quibble. I really would prefer that they use the titles for me and my husband, although I'm not sure it will ever be important enough to do more than just refer to myself that way (like when I sign their birthday cards).
My husband's sister's older son gets regularly chided by his parents to not drop the title when talking to or about me. He's very consistent with titles for everyone except me (because he lives in my husband's home country), so it is kind of odd that he doesn't use it consistently for me. To his parents, it's a sign of disrespect, so even if I wasn't particularly bothered by it on my own account, I do remind him to call me "[Aunt] Dindrane" when he slips. And truly, I rather like the title. Being someone's aunt is a special thing, and it gives me warm fuzzies to have people refer to me as such.