This is timely, because my MIL's nickname (really the only name that she goes by) is the same as mine, so DS grew up calling her "Grandma Terri" so, to avoid confusion, once DS has a child, I'm going to have be something other than that (presuming she is still alive). I'm rather fond of "Nana" because it reminds me of the dog in Peter Pan (I love Newfoundlands)!
Terri