I run Net on my t420, and I like it. I feel like I get ~3 hours (I don't keep hard time) using it, and it'd be fair to say typical use is development, w/ web (ie: running X, vi, clang, and various text-processing tools, Firefox, and disk/network intensive things like syncing code-repositories).

I've got a 9-cell battery.

I'm running -current. Now that -current is also offloading rendering to my integrated i915 gfx, I'll be curious to see how screen-intensive work will impact battery.

The joy I get from NetBSD has outweighed various temptations from other OSes. I've dabbled w/ Ubuntu and others, but they're not compelling enough to switch.

If you've got any questions, I'm happy to try to answer.