As long as Sony doesn't make the OS too big the 4Gb of GDDR5 will be very nice if it's all available to games. These specs are really interesting because when it comes to multiplats there will be areas where one differs from the other but it'll be really close. Exclusives will look pretty damn different though because of the different strengths of the systems. Both systems sound powerful but with different strengths. People from both camps should be happy.
I believe Sony will limit the OS to around 1 gig at most, and more likely 256-512 MB.
Vita I believe reserves about 256 MB and it pretty much has all the features Sony looks to be trying to hit -- cross game chat, psn store mid game, browser mid game, etc.
Sony's OS is going to be pretty simple with features most gamers will care about.
I think MS is going to go all out on OS features (where having 8 gb of ddr3 helps tremendously), with win 8 tie ins, perhaps some unique video recording abilities, and quite a bit more multi tasking during gaming sessions (perhaps stuff like pulling up cable tv mid game or split screen). Their hardware design seems to reflect that - great for accomplishing a lot of various tasks, but not completely devoted to gaming as the overwhelming priority.
Sony on the other hand looks to be positioning their console power priorities almost entirely on what will affect gaming performance.