As I mentioned before, I'm really liking the ThinkPad X300. My only real gripe at the time was the lack of battery life. Well, last week I got the 3-cell "Option Bay" battery (which replaces the optical drive), and today I finally got the 6-cell replacement "main" battery.
As I'm typing this, powertop says I have 5.8 hours remaining, and I've been running for 24 minutes. So not exactly the 10 hours advertised on Lenovo's site, but, hey, definitely not bad.
I'm taking this thing to YAPC next week, so after living with it for a week, I should be able to do a full review.
Oh, and according to the shipping scale at the shop, with all 9 cells worth of battery, the X300's total weight is up to 3.5 pounds.