If you haven't been there, thinkpads.com
has a good forum
. I haven't seen the T42p screen, but I know in the past there was a compromise between the flexview and non flexview screens. The flexviews had good contrast, but slower response. I haven't kept up to see if that has changed. We have a T40 and flexview A30 at work and they are nice machines. However, I can't say their panels are great, but they aren't the latest machines either.
The T42p/T43p and i9300 are really different machines. The T series is really portable, great keyboard, both trackpoint and trackpad, gigabit ethernet, workstation video card options and non wide screen 14" & 15" screens. The i9300 is a much larger machine including the thickness. It has decent internal speakers, trackpad only, almost as good keyboard (at least one of the two they use), DVI output built in, high-end gaming video board option but no gigabit ethernet. I think the T43p will offer ExpressCard, but I don't think the i9300 will. As far as screen size, the 17" widescreen height is the same as the 15" non wide screen - 9".
I think the Dell latitude and workstation lappies are more direct competition. The new 610, 810 and M70 look interesting. The present M60 uses NVidia Quatro video cards, which many say are much better than ATI for open GL apps, such as 3D CAD.
How thinkpads and their support will change with the sale to Lenovo (if it actually happens
) remains to be seen. The company I work for just dropped IBM for the desktops and switched to Dell. For now, I think the thinkpads will continue their level of quality, but at the historical price premium. Dell's newer lappies (i700m, i6000, i9200) have improved build quality over the previous inspiron models.