According to a Polish person I met last night Poland have no regional accents at all and it would be impossible for her to tell where someone was from by their accent.
I found this pretty strange. The only other country I can think of that lacks regional accents would be Australia where it's pretty much just a rural/urban split in the accents: you couldn't say if someone was from a particular major city by how they talked.
Does anyone else find this remotely interesting? Probably not.