Honestly, I'm disappointed they still haven't incorporated a second USB port. No matter the upgrades made to the SP3, that was the one I was looking for. That being said, they did address one issue I have with the SP2: Vertical work space. As a fledgling programmer, it's sometimes frustrating being limited to working with so little visible code at a time.
Beyond that, I'm in love with my SP2. After calibrating my stylus, the accuracy improvement of the n-trig stylus isn't a selling point. Inversely, the battery in the SP3 pen is a deterrent. Also, I love the magnetic connection between the SP1/2 and the Wacom pen. It's so dang handy, and I use it constantly. I tried the fabric holder for the SP3, and dislike it greatly.
So, what is left for me are two very comparable products.
-SP2 is more portable, though heavier (a definite down side).
-The i5 CPU's are the same (with minor differences), thus speed is near-identical.
-The MS capacitive button is ideally placed on the SP2.
-Many of the bugs associated with the SP2 hardware have been addressed (most recently the WiFi vs Bluetooth issue). A new SP3 owner will have to face new SP3 problems.
-Finally, the kickstand is preferred on the 2. "WHAT!?" you ask? I am constantly toggling/switching angles of the SP2, and I've accustomed myself to doing it with a single finger and a single hand, an action I was not comfortably (or at all) able to replicate on the extremely resistive SP3 kickstand.
So, I say to you all that I am very pleased with my SP2, and look forward to seeing what the SP4 has to bring to the table. At that point, provided it has (at least) two USB ports, I may consider upgrading.
Hope this helps. =)