Andrew from HotHardware takes a detailed look at the ultra-compact ThinkPad X41 Tablet system. Here's a snip from his review:

Measuring in at 10.8" x 9.5" x 1.1~1.3" and with a weight starting at 3.5 pounds (our T43 sample weighed at 3.5 lbs. with a 4 cell battery), the IBM ThinkPad X41 Tablet PC is the first Tablet design to emerge from IBM. From the name, you can already deduce that this X Tablet series is an offshoot from the ultra-portable X series of ThinkPads. For those highly mobile (~70%+ of the time) and those needing the notebook like qualities of a Tablet PC, the X41 Tablet PC fits the bill..



Link: HotHardware