I'd challenge you to geographically place my english accent. Some people say Oxford, some people say Hampshire, neither of which I've actually lived in
http://www.planetary.org/radio/show/00000251/ (I'm the guest, from a few mins in)
I wouldn't even try - I'm American, so I can only distinguish the really obvious dialects, like Yorkshire or Scouser. Some accents are certainly more generic than others, to be sure. I find that people in the UK are more attuned to placing a person regionally by their accent.