I like it! I use it all the time. I should probably say that I’m running a kind of minimal environment on the R-01 DevTerm: lightweight UI (ratpoison, conky), some small programs (urxvt, xpdf, lighttpd, w3m), and most of the time it is connected to another machine that is doing more work (drawterm to the Plan 9 systems, ssh to the Linux systems). I run gcc and the go compiler sometimes, I use awk a lot, Ruby once in a while.
All of that stuff that I have up and running, the CPU sits at about 3% used, using about 150MB RAM. Because of that, the batteries last 6-8 hours (depending on how I set the backlight), and this is incredibly useful.