At certain new technology introductions you need to start making cut-offs of machines not meeting future requirements. A Thinkpad if well kept will most likely be still useful 5 or more years from now, so it's wise to buy something more future proof.
For instance in 2005/6 the cut-off for me was: USB2.0, SATA, ability to run Longhorn (DX9, 1-2GB of RAM). Now I would add to the cut-off the 64-bit CPU and ability to add 4GB or more RAM in the future. Thus I would not recommend getting a T4x (T42p, T43p have DX9 but they're very old by now) or T60 (3.5GB RAM limitation). T61 is the minimum. Of course there are exceptions to this rule (if you want 3:4 IPS then it might be worth sacrificing 3.5GB RAM limit for UXGA IPS in T60p but you'd have to upgrade CPU to run 64-bit Windows).
For about about 450 Euros you can get a used good condition still in warranty 14" T61 with 1440x900 resolution. It will most likely run next version of Windows (8GB RAM limit, 2TB HDD limit, Microsoft probably won't change DirectX requirements for next generation desktop). I recommended new 14" T61 with dock to similar friend (small room, big noisy desktop with CRT) couple of years ago and she loves it, also ordered used mint in warranty 14" T61 for my brother.
If someone is about to buy new machine and can wait it might be worth to wait for next generation as those bring USB3.0 (not as high jump as USB 1->2 was), UEFI (support for booting beyond 2TB HDDs, other changes), SATA 6Gb/s (some SSDs are already requiring it, at the end of life of this machine fast SSDs will be ubiquitous). The 15" workstations will probably get 3D and we might see IPS again.
T540p, T420s (soon to be T420ps
), X61t, T60p, T42p, A21p