So, summons are now tied to specific characters. Each l'Cie has the ability to learn to summon a unique monster as they unlock their powers (won't be availible when you first get them, only as they progress through the story). We know that Snow has Shiva, and now it is revealed (in Playstation, the Official Magazine) that Lightning has Odin. Also, transformations will play throughout the summon system, so Shiva's motorbike form won't be the only one.
Apparently they're keeping FFXII's idea of summons lasting for a limited duration, and instead keeping them around until they take a certain amount of damage, so if you play things right, you can keep them around for much longer than they would remain in FFXII. The transformations require a new resource (TP, I think it was, don't quite remember, and information was deliberately vague on it) to trigger them, and they switch the combat from a semi-turn based into a more action oriented style.
So, how do you all think this system will work compared to those of the other FF games, and which summon do you think will be paired with the remaining characters (assuming they are all l'Cie, which is likely)?