“Today, the Raspberry Pi Foundation announced availability of their new board called Raspberry Pi 3”
From expert reviews;
The Size and layout of Pi 3 (left) has a slightly different board layout to the Pi 2 (right), although both are the same size.
One should be able to swap out an old Pi 2 for the new model because Raspberry Pi 2 and Pi 3 are of the same size (86mmx56mmx21mm). There’s a board layout differences that may cause problems due to the power and activity lights on the Pi 3 have been moved to the bottom left of the board from the top left on the Pi 2. If your Pi case shows these lights, they won’t be visible if you upgrade to a Pi 2.
Both models have an integrated microSD card slot, but the Pi 3 has a friction slot, rather than the spring-loaded slot of the Pi 2.
Pi 3 has built-in 802.11n Wi-Fi and Bluetooth which are the new features.
In terms performance and energy consumption, Pi 3 has lower power consumption, a faster CPU, quicker graphics core therefor can run more complex tasks since Pi 2 had a 900MHz Cortex-A7 chip, but the Pi 3 has a 1.2GHz Cortex-A53
see Pi 3 video illustration below;