The only association I have with the name Poppy is that's what we called my grandfather growing up :)
When i was younger i lived in england and there was a sweet new baby girl named Poppy and she was precious! nothing but sweet memories for this name!
I've no idea why Poppy would be considered unusable. I'm assuming you're in America because it's a very popular name in Britain, Australia, New Zealand, etc. I know a baby born recently on Anzac Day (April 25) who was named Poppy in honour of the day! NB: If you don't know, Anzac Day honours soldiers who fought in wars for Australia and New Zealand. The poppy is the symbol of the day. I think it's a sweet name, although it's rather cutesy.