Always, ALWAYS wishing I had more power. On the plane, at the pool you name it. Purchased the 2nd to largest one of these:http://www.hypershop.com/HyperMac-External-MacBook-Battery-and-Car-Charger-s/91.htm
and am really happy with it. It's Mac only for power, but dyno for USB applications as well. kept my MiFi, phone and computer running full charge while out at the pool. Yes, the downside is that my dorkigeekiness has gone *through the roof* because it's no longer just a notebook, I now have a full rig at the pool (and between that, my Tilley hat and my need for umbrellas, I have virtually assured my lovely PinkHat that she will never need to worry about another woman) and am even getting a tiny amount of work done ... although my penchant for Binga Bangers has slowed my progress substantially. But I digress.
Batts are moving forward nicely, and they're worth the flow now IMO.