For a laptop that small and meant for portability, 5 hours is pretty bad.
Potentially, yeah. It partially depends on how much the drivers are optimised - for example, the current 13-inch Macbook Air only manages ~4.5 genuine (Windows) hours power saving out of a 6600mah battery. The X201T manages ~5 genuine hours power saving out of a 4600mah battery.
Assuming the X1 cell outputs 14.4V, 38.4wh means a pathetic 2600mah battery. Even with Sandy Bridge and all sorts of Battery Stretch trickery I don't see anyone getting 5 hours out of that.
Anyhoo, I'm hoping that figure is wrong.
I haven't tested it yet - but the battery meter usually tells me I have 3-4 hours from a full charge. Admittedly, it does seem to charge a lot more quickly than other Thinkpads, but if you are going to be away from an outlet for a while, you'll need the additional slice battery or some other power source.