The Ingress app was updated to version 1.23.1 today. The changelog indicates that this isn't a massive overhaul to the app, but it does mention that in addition to power cubes being enabled, we also have some minor bugfixes as well as improved visual effects. We don't know everything about power cubes just yet, but here is what we know so far:
Power cubes are a concentrated form of XM and they can be used to recharge or power either a resonator or possibly even a portal. We do know that there are various levels of power cubes. It could be that a given level of power cube can only be used on a portal or resonator of the same level, or it could be that a power cube simply charges anything with in a certain range and a higher level just means that the cube will have a greater ability to charge. At this point your guess is as good as mine. There have also been rumors that there might be some offensive weapons being added in the near future. I could see some type of portal mod that would give that portal an increased ability to drain an enemy that hacks or attacks that portal. Especially with portals that are tightly packed together this could be a cool strategic tool. If you were to give each portal a shield, a power cube, and an offensive weapon any player from the opposing faction could end up in serious trouble if they attacked with several portals in range. It would be cool to be able to drain even a high level player in just a few seconds with enough upgrades to enough portals. Of course these upgrades would have to be somewhat rare, or else portals would stop changing hands, and that would pretty much defeat the purpose of the game.
I'm sure we will see a few more surprises between now and whenever Ingress leaves beta status. For some more details on the game you can check out the Ingress Report video below. These are a tad cheesy, but it is cool to see how Ingress is bringing people together all around the world. You can subscribe to the Youtube channel to get weekly updates.