Several major changes came to 0.0 with the new Dominion expansion. Some good, some bad. Having now spent time claiming sov with the new system as well as taking part in a war to take sov from another alliance, I now have a good idea of how the system now works.
The idea that the POS slog is gone from Eve is not true. High end moons are still the bread and butter of alliances, so removing POSs from those moons is still the focus of wars of aggression. Wars move a little faster and there are less POSs to kill. In Dominion, alliances do not end up in a race to see who can place the most deathstars and resistars (and who can kill the most). This had been the single biggest problem with the old sov mechanic. It was the Eve equivalent to trench warfare. It led to static wars where the only way to win was by attrition (corps leaving, players not playing, or meta gaming to break apart the alliance).
However, something crept in that now tips the scales heavily to the aggressor. It makes defense near impossible in major conflicts. Fleet lag. When the numbers swell to a few hundred on a grid, ships entering the grid will sometimes wait tens of minutes to load the grid, let alone the half hour or more when a thousand man fleet moves. This means an attacker need only bring a few hundred ships and get on grid before the defense fleet shows up to turn the game into shooting fish in a barrel.
This is obviously a problem CCP is trying to fix, but at this time, the attacker is favored, so sov is changing hands at a rapid rate.