So, I bought a new laptop. It's a Lenovo X220 Thinkpad and a pretty nice machine. An Intel Core i7, 8 GB RAM and a great keyboard. A shame it's got a touchpad since I only use the trackpad (like on my X60s): I disabled the touchpad in the BIOS.
I initially tried to install Debian Stable (Squeeze) on the machine, but the display resolution was wrong because X wasn't new enough. So, I installed Debian Testing and ran with this for a few days. Mostly OK but at least one solid lock-up a day and no error reports in systlog or Xorg.log.
This is very new hardware, and from scanning Phoronix (for example), I know a lot of Intel DRM work (both driver and kernel) is ongoing. So I downloaded Linux 3.0 (rc4, then rc5) and made a kernel package in the Debian way :
So far, so good. No nore lockups.