My experience with ThinkPads has also been good (albeit, my hardware is much older). I've used CentOS with a 760XL and have put Linux onto other older systems as well.
Best recommendation I can give is to use Google to search out other's experiences with the specific model; also use sites like TuxMobil and Linux-Laptop.net. TuxMobil covers non-Linux environments as well; Linux-Laptop.net does not.
Also, Linux is much more likely to support all of the hardware and to work out of the box. This is not due to any fault of BSD, but to the popularity of Linux, including manufacturers that help support Linux.
Even so, FreeBSd will work on many laptops, and OpenBSD has better support for wireless than any other distribution out there (possibly including Linux).
Also, if you have limited memory in the laptop, use a Linux distribution that uses a lightweight desktop (such as XFCE, Fluxbox, IceWM, or WindowMaker). Switching to FreeBSD will also help: the BSD environments are smaller than Linux generally. Stay away from OpenSolaris if memory is tight or if the system is unsupported: again, not because OpenSolaris is bad, but because it doesn't have the popularity, the drivers, and so on - and is just plain larger than the others.
One more thing: when done, document what you did and how and what your experiences were - and post it to the Internet for people to learn from your experiences.