I think what is often overlooked in selecting a laptop is DESIGN!!! You can't buy a notebook with the same mindset as buying a desktop.
Lets compare the IBM T40 to 2 other notebooks mentioned around here: Dell 600M and Presario X1000
First if you configure either the 600M and X1000 with the same 3 year warranty and Windows XP PRO that is standard with IBM, their prices come out to be very similar to the T40.
Now on to the DESIGN.
Thickness: The IBM is 30% thinner than the 600M and X1000 1 inch vs 1.3 inch. While on paper this may not seem much of a difference, visually and ergonomically, the difference is huge.
Weight: For me personally, I think anything over 6 pounds w/ the CDRW drive installed is too heavy. Notebooks are meant to be portable. The weight becomes very noticeable once you go over 5.5 lbs (IBM T23). While the 600M claims to be ~ 5 lbs, I think it's a big lie. Dell is not very forthcoming when it comes to specifying the weight of their computers. I had a 600M that I ended up returning (I got it for ~$900 with CDRW/DVD included too), and it felt very heavy, combined with its thickness, it seemed very clunky. The compaq X1000 is rated at 6.8 pounds. As a nice comparison, the Apple 17" widescreen powerbook is 6.8lbs and the 15" wide screen powerbook is ~ 5 lbs. Thus the X1000 is going to feel quite heavy.
Casing/Durability/Rigidity: These specs are rarely compared. The IBM T40's casing is super sturdy, built to last, though some say the older T23 was even more sturdy. When you pick up the T40, it feels very solid, no creaking sound or anything. It feels like you are holding one solid piece of material, and not like 3 pieces hinged together. The casing on the T40 is titanium and is very strong. Even when you press hard on the back of the LCD, the screen does not distort. One of the huge benefit of a good casing is the psychological peace of the mind that you get from carrying around the notebook, knowing that it will not be easily damaged. I remember someone once said "If someone was trying to steal your thinkpad, you can use it as a weapon to fend off your attackers and still file your police report on it right after.
As for the Compaq, it is mentioned to have aluminum casing, but I don't know whether it's aluminum all around of just for the LCD casing. If it's 6.8lbs, I think it may be quite sturdy.
Other the other hand, the 600M is a POS when it comes to its casing. It's pretty much plastic all around. The LCD distorts easily even when you just touch the side of the screen, let alone pressing on the back. Do a google search on "dell 600M rippling" and you'll see what I mean. When you pick up the 600M, it makes creaking noises due to the plastic casing bending. When I was holding my 600M in 1 hand, I felt as if the notebook was going to snap in half. What does this mean if you carry around your notebook a lot? It means subconciously, you are going to be constantly worrying about the possiblity of breaking the laptop.
Style: This is where PC users have often made fun of Apple. While I could care less what my Desktop look like, I consider the looks of a laptop very important. There is more of a "gadget" aspect to owning a laptop. Apple and Sony have long been the coolness leaders in notebook design. IBM's notebooks are geared more towards business users, and thus have a more conservative, but still very sleek design. Dell notebooks looks freaking ugly in my opinion. Have you noticed Dell's website often only shows only partial angled views of their notebooks? I bet it's because that is because if they showed their notebooks in its entirety, people will realize how ugly and clunky the notebooks are. The X1000 looks OK from compaq's wbsite, but I want to see close ups and shots from various angles.
THe bottom line is that when buying a notebook, you are not just buying the cpu, HD, ram, GPU etc. The price tag reflects much more than just the pure hardware spec.