This is a bit subjective, but the Thinkpad T41 (with 40GB drive) looks to be a bit unreliable. Getting replacement disks looks to be a real pain in the neck. The good news is you don't (necessarily) need IBM though.
For the uninitiated, the IBM Thinkpad T40/T41 machines are really very nice indeed. They have loads of great features, and look to be pretty tough (certainly their predecessors like the T21 and especially the 600 range were good).
Previous models came shipped with a "recovery CD". This CD was (for all intents and purposes) a clone image of Windows that could be loaded onto the machine (thus losing all the data, but installing "factory fit" windows). The recovery image, or the initally shipped image of Windows wasn't bad - unfortunately only a single partition, but contains all the right drivers and toys to make the Thinkpad work. For business use, we tend to remove a few bits, and configure a few things differently, but all in all, it's pretty good (if you're just getting into this - you can almost certainly strip out vast quantities of stuff in the IBMTOOLS directory).
On the T40/T41, the recovery CD is gone. Instead, there's a hidden partition on the hard disk. It's completely inaccessible from the OS because it's enforced by the Bios. There's a Bios option that turns off this protection, so you can use the whole disk if you want (provided you don't mind losing the recovery image). If you do have it though, then you can just boot into it (via a Bios option) and rebuild your machine, losing the data, in about 20 minutes (and about 15 reboots). Again, pretty good.
This hidden partition is potentially an IBM stitch up. If your disk fails (as they seem to be doing frequently in our recently purchased batch of T41s), then you'd seemingly have to get IBM specific replacements (after all, no one else will put the recovery partition on the drive, right?).
If your Thinkpad is on warranty, then you can call IBM Service & Support and just get a new one sent to you (it takes a couple of days, but they'll also pick up the old one from you). However, having just taken delivery of a replacement, I found it doesn't have the recovery partition on it (despite specifically ordering the correct FRU part number). A few calls to Product Specialists reveals that replacement disks don't have the recovery partition on them. Service & Support have to send you a CD which puts that partition back on the disk.
If you look after a few T41s, you may be thinking about getting a spare drive to replace all the failed ones a little more rapidly than you could do using Service & Support alone. If you order the drive from IBM, it could take up to four weeks to be delivered (unless by some miracle they have stock). Alternatively, you could use an 'ordinary' drive from any supplier you like, probably delivered to you in a day or two, and simply apply the recovery image.
My advice for any T41 owners: If your hard disk fails, get a replacement from IBM but make sure to ask for the recovery CD that puts the hidden partition back (they may not ask you, and won't send it unless it's been explicitly requested). If you want it done a bit quicker than that, buy a drive from your favourite supplier and use that (along with the recovery CD). Since we use Ghost images we don't immediately need the recovery partition, so we can get moving quickly. We'll need those partitions back on the machines when we come to sell them on though, so it's worth thinking ahead.