Macworld UK reports that UK bandwidth restrictions may negatively impact Airport Extreme use in that country. Airport Extreme uses both the 2.4GHz and 5GHz frequencies to communicate. In the UK, Japan, Austria, Estonia, Germany, Latvia, Slovakia and Spain, regulatory restrictions prohibit wide-channel operations, so Airport Extreme users won't be able to use part of the 5GHz frequency. Macworld's article suggests that this puts a limit of a 2.5x speed increase over 802.11g rather than the 5x increase that's achievable by using the entire 5GHz frequency with 802.11n. It's hard to say how noticeable this will be in practice or whether users will be able to "work around" these restrictions. Anyone with better knowledge about how channel operations work and how wide-channel restrictions will affect performance, please jump in in the comments.