From what i remember learning in school, the seats of government of viking age Denmark and Sweden were Jelling and Old Uppsala respectively. Both of these cities lay close to the sea, with Jelling near Vejle fjord and Old Uppsala near Lake Mälaren (which drains into the baltic), but neither lies on the coast. Wouldn't the distance hinder preparations for raiding if the ships had to be kept in a different locale, seeing as the seat of government didn't have a port directly into the ocean? Did they have separate port cities for housing the ships? Did religious aspects, such as important religious locales, also influence the placements of the seats of government?
Im not sure about Jelling, but Gamla Uppsala originally lay at the sea but the land level rose there due to isostasy, moving the shoreline further away. Isostasy is a geological term for a post-glacial rebound. When under the glacier (which is quite heavy) the land sinks down, and after it melts it will slowly but gradually "float" back up again. There are more examples of Norse villages that used to lie at sea but are actually inland today.
Isostasy is a major concern in the global warming problems of today. Not only will melting of the Greenland glacier raise the sea level - the land beneath the glacier will also rise, raising the sea level further. In southeast Iceland, there has been a few centimeters rise due to Vatnajökull glacier having become thinner.