Ask HN: Current state of Geo-IP?

I'm trying to weigh the cost/benefit of adding some geo-targeting to a client's ecommerce site. In my very limited testing (6 regionally diverse tests) I'm only getting useful regional information 50% of the time. (National info isn't useful for this client).

I was wondering if there was good data out there, or at least some better informed opinion on what results can be expected.

Thanks!