What is difference between English Windows 7 localized with language pack and "generic" national edition? SKU on the box, I know, but will be there any differences for average end-user? In US Win7 will be much cheaper than in Europe...
With Vista and above, there is no difference whatsoever. Localized national editions are just Windows 7 with preinstalled language pack.
However, I am not sure whether buying software in US is in accordance with importing laws of your country.
One difference you will see is with the media since you can't localize that part. This means that your installation/setup will always be in english.
My experience from Vista tells me that you will run in to a few problems with the language pack option.
For example, you cannot install the english service pack when they become available because they're not compatible with the language pack you have installed ( not a big issue but can be a source of confusion ).
You can be required to install the english version of IE when IE9 comes out and then install a language pack for it. ( not a big issue but also a source of confusion ).