Based on what we know so far:
PS4's GPU ~50% more powerful
PS4 has access to more memory - 7GB vs. 5GB of XBone
PS4 has upgradable HDD
PS4 allows the sale/trade/sharing of games
PS4 doesn't require 24 hour internet check-in
PS+ is $10 less a year and offers better perks than Xbox Live
Most likely PS4 will sell far better too which means most likely more exclusives on PS4 long-term.
MS needed Xbox One at $299 and yet they priced it at $499.
I also bet most Xbone exclusives will be XB1/PC, which means if you get a PC + PS4, the XB1 is completely redundant unless you can't live without Gears and Forza.
Nintendo will likely drop the price of Wii U to $249-279 once PS4 launches, leading the way for casuals/budget gamers while PS4 will capture the hardcore gamers, leaving XB1 in no man's land. It's hard to comprehend how MS messed up this badly. If anything they could have made the most powerful console, with the most features and undercut Sony without trouble since they can afford to, while Sony is losing $ which means it's much harder for them to undercut a financially strong company like MS.
Facepalm MS.