I just setup Linux on my T40.
I've tried various versions of Linux on multiple types of thinkpads starting with redhat 5.x on a thinkpad 760, the 760 was like brick. As the years go on the install gets easier and easier - but there's always a little something to stop me from using it as my main OS. Either the USB support is not up to scratch or, more recently, wireless isn't easily configurable.
I like Linux, but I still believed it was more suitable for servers rather than workstations and laptops because of the sheer quantity of fidling required to get it to run all the apps I need. I have an RHCT certification from Redhat, but still have more than the one or two issues with linux, however no more issues than when i was learning how to maintain windows.
Well, I finally found a version of Linux that does what i need on my laptop.
Suse 9.2 Professional is superb. Suse 9.1 was a lovely install - but it didn't do wireless. Suse 9.2 supports wireless effortlessly - it installs without hastle, the default disk partitioning will setup an existing windows disk for dual boot by deault (do a backup first).
I have VMware 4.5.2 installed - this was the only difficult part of the install - i had to search for all of 10 minutes to get a resolution to my problem before resolving it. Now it works perfectly.
My next steps are to get my companies VPN software to operate so that i can access the intranet and to get Lotus Notes working under Wine (yeah I know, a native version would be good). In the future I'll be working to get the IBM Workplace Rich Client working under Linux - If you are vaguely interested let me know.