This thread was originally just talking about online table top gaming but I figured it might as well serve as the 4th Edition catch all.
So here are the details you need to know!
D&D's 4th edition is being released June 6th, 2008.
The major changes in this release are:
* Character levels going to 30
* Better defined character roles
* Better defined monster roles (brute, soldier, artillery, controller, lurker, skirmisher)
* New monster statuses (Minion, Standard, Elite, Boss)
* Streamlined combat
* Streamlined leveling
* Online tools
* A larger list of changes can be found here and here.