If you get error 002-0102. Yep, you can still purchase games or downloadable content, and use Miiverse. You just can't access services that use the Friend Service (such as the Friend List and online functions in games).
But if you get 022-2812 when accessing Nintendo Network services, or 002-0121 when accessing the Friend List, then you can't use any Nintendo Network service, including the Nintendo eShop (which would result in 002-0121 if accessing without a NNID, or 022-2812 when accessing with a NNID).