Xbox One Pros:
Extremely fast switching between tasks (TV, movies, skype, etc.)
Kinect seems much improved with 1080p quality and more accurate tracking
ESPN partnership
300,000 servers for Xbox Live, according to Microsoft this will allow for "living and persistent worlds" (MMOs, anyone?)
Controller seems mostly the same except with improved d-pad
Compatible with Smartglass
Constant low power state
Download games while you play
Capture and editing software (very lightly touched upon during the event)
Kinect voice commands (useful for when you're holding something, such as food)
Triggers have feedback
Xbox One Cons:
Used games fees (Lots of conflicting info at the moment; policies not finalized)
Requires a connection to the internet once every 24 hours Source[1]
Significantly less powerful than PS4 (Source 1[2] , Source 2[3] )
Kinect is apparently required to use the console (conflicting reports)
No Backwards compatibility
Most likely going to have to pay to play online
Microsoft will not allow indie devs to self publish (for XBLA, if XBLIG is carried over this will be possible, also, Microsoft is apparently working on a plan to allow ALL creators to "be a part of the future of Xbox One")
Microsoft has not talked about how or if services like their TV, Music, and other services will work outside of the US, as there are usually complications involved with that kind of thing
Kinect voice commands could possibly used by others to troll or other shenanigans[4]
5 gb ram available to devs Source[5] 3gb ram reserved for multiple OS and system ressources.
PS4 Pros:
You can play games/demos while they are downloading
Pressing a button puts the console into "low power mode" and when pressed again pick up right where you left off
Share button lets you capture footage and upload it (dedicated capture/compression)
Ability to stream games to friends
8gb GDDR5 Ram (7gb available to devs)
Dualshock controller seems larger and the triggers/analog sticks seem improved (touchpad added, but I don't know if I consider that a pro or con)
Sony lets indie devs self-publish games, making it easy to get on the store
Cross-play with Vita
Compatible with PS Move
Download games in the background
GPU 50% faster than Xbox
Mobile app that will tie in with PS account
PS4 Cons:
No backwards compatibility (Will be able to play older games through Gaikai)
It's been hinted that publishers might be able to choose to block used games
for your information