The Raspberry Pi 2 Model B is out and it's amazing! With an upgraded ARMv7 multicore processor, and a full Gigabyte of RAM, this pocket computer has moved from being a 'toy' to a real desktop PC!
The big reason to upgrade to a Pi 2 Model B over a classic Raspberry Pi Model B+ is the big boost in performance
The Pi 2 has 4 processors in one chip (the B+ has only one), an ARMv7 core vs an ARMv6, and 1 Gig of RAM vs 512 MB for the model B and B+
Those 3 improvements translate to pretty big performance increases!
OK but how much faster is the Pi 2 vs the Model B+? While it strongly depends on what you're doing, you should see at least 85% improvement (single-core processes that just depend on the ARMv7 vs ARMv6 upgrade. For anything that can take advantage of multi-core processors, you can see up to 7x increase in speed!
Using the Pi as a computer feels fast and 'desktop like' - not sluggish! Particularly for developers, compiling code on the Pi 2 is 4x faster and the extra RAM helps a lot too, so most programs can now be compiled directly on the Pi.
The Pi 2 keeps the same shape, connectors and mounting holes as the Raspberry Pi B+. That means that all of your HATs and other plug-in daughterboards will work just fine. 99% of cases and accessories will be fully compatible with both versions
Please note: The new processor on the Pi 2 means that you will need to create a new SD card with your operating system (Raspbian, Arch, XBMC, NooBs, etc) because you cannot plug in cards from a Pi 1 into a Pi 2. Also, any precompiled software will not work at full speed (although supposedly the processor will be able to run it). Still, you'll want to have it recompiled for the new processor! For many people, this isn't a big deal, but if you have a pre-created Pi 1 Model A+B+ card image, just be aware it won't work!