dm1z 2.4 GHz WiFi only, Lenovo offers Thinkpad x120e option for 2.4GHz/5GHz 2x2 a/b/g/n wireless LAN adapter for $20

From the Lenovo site you can customize a x120e with a 2.4GHz/5GHz 2x2 a/b/g/n wireless LAN adapter for $20 extra:

Integrated WiFi wireless LAN adapters

• ThinkPad 1x1 b/g/n [base]
• ThinkPad 2x2 a/b/g/n [$20 upgrade]  

This is a good option and you should get the upgrade for sure if you're buying the x120e. I was looking closely at a x120e but went with the dm1z. I did not realize the dm1z wirless adapter didn't support 5GHz at the time of my purchase decision. 5GHz WiFi is the way to go even though it is not as common right now. Not sure why HP cannot add a similar option for the dm1z. I would've paid $20 extra for this had it been offered. I'm looking at 5GHz wireless adapter options for the dm1z now. I do still highly recommend the dm1z but this is a factor in any buy decision if you're comparing these two units.

[UPDATE]
Lenovo no longer offering 5GHz WiFi card option for x120e