I do work at IBM. the T42 has been handed out like candy under the laptop replacement program. I was upgraded prior to the T42, so I didn't get it, i'm typing this on on R50.
The T42 has the Pentium M, which is a good processor, but it's not as fast as the core duo, but certainly faster than the G4. it's also still a hot machine if you run it with all timers disabled/full clock speed. The nice thing is you can get the 9 cell extended battery and get 5 hours of REAL full clock speed performance (under normal condition, not running a graphic intensive game).
All in all it's a great machine, people haven't had problems with them (unlike the R50s/R60).
I'm not telling you this to sway you, just to give you some real world (visual) experience on the thinkpad.