I got a few minutes with the iPad Pro at my local Apple Store. No where near enough time to evaluate day to day use, but here are some quick thoughts:
Bigger than you might expect. When drawing with the Apple Pencil the large screen made for a great canvas. Just using the stock Notes app was great, but for things like the home screen grid of icons, the screen felt underused.
While it seems light for the size device you're holding, the weight might prevent extended reading sessions or movie watching if it's not leaning against something.
It works remarkably well. I'm no artist by any stretch, but my handwriting with a fine tip pen looked just like my writing on a piece of paper. Even switching to the "pencil" mode in notes looked like lead on paper.
I instinctively flipped it around to erase something, as you would an actual pencil, but no dice. There are no sensors in the top end of the Pencil, just a cap covering the charging port.
The Pencil was actually dead when I first tried using it, but just a few seconds plugged in to the iPad lightning port got me several minutes of use.
Apple's new Smart Keyboard cover leaves something to be desired. My $50 Logitech Keys-To-Go has a dedicated Home, Multitasking and Spotlight button, which come in handy. Apple's keyboard has none of these, and the letter keys seem a little too far apart.
If I were to get an iPad Pro, the Apple Pencil is a must have accessory, but I would stick to my full iPad case and third party Bluetooth keyboard setup.