I just got the PowerCover. I'm so pleased with it - it looks like for my usage, my SP2 can last about 12 hours. I also do like the 10" form factor, though the SP3 I held at BestBuy was REALLY nice. I really like the new pen as well.
But I decided to invest about $250 on my SP2 and make it the way I want it. I'm hoping the new Core-M processors will debut in some form by end of next year and get a SP4 (or SP5) when those are out. Right now, I got a nice case to make it easier to hold the SP2, and I have a Wacom Feel pen for the SP2 that gives a pen experience much more like the SP3. I really hate the SP2 pen for writing, the feeling of hard plastic on glass doesn't remind me of actually writing. The Wacom Feel's pen is like the SP3 pen in that it is much more like felt.
BTW, I noticed a lot of wear on the nib of the SP3 pen at BestBuy after a few days. This is a downside of the softer nibs, but I personally would rather swap them out all the time than take hard plastic vs. glass. Ugh.