Not really sure what Aaron means about the tracing thing (Or why his paranoia isn;t equally valid under SR4

), but I can try tackling Decking for you...
Basically, Augmented Reality. AR gives the world a "VR Overlay" that everyone interfaces with. Hackers, however, can do a lot more with this overlay. Basically, it makes the Matrix "out there" for the decker to interact with. So for starters, it means there's no reason to stay at home in the basement while you Deck. That's the flavor stuff, anyways.
Now for rules. For starters, the rules are cleaner and pretty simple (though I will admit/agree that the Matrix section is somewhat cluttered). Fewer things to keep track of, fewer rolls to make, on behalf of both the player and the GM.
The second is that everything happens in "Real Time" rather than that goofy "Matrix Time" that used to exist. Matrix Time (Speed of thought stuff) was never really defined well, was confusing, and just really made decking a pain in the arse to deal with.
The third is that it's usually easiest to interface with a node or network directly, rather than hacking your way through a chain of nodes. So the hacker goes ON the run with the other PCs. You come across a locked door? Hack the lock. Security cameras a problem? Hack the buildings security and turn them off, or edit them to recieve a feedback loop. Sec guards got you pinned down? Hack their personal commlinks and feed them some false location data on you and your party.
Bull