I have a ThinkPad X201 convertible with the 12" 1280x800 touchscreen. (The screen's nothing amazing; rather dull.) But it's a great device, apart from the repeated fan weardown (replaced 3 times already) which makes it get a bit hot. If Lenovo made a decent upgrade, I'd buy it in a minute.
Anyways, I've noticed no problems working on the 12", other than the lack of pixels for virtual size (like IDEs and stuff). A 1080p resolution fixes that.
1080px is a downgrade for me - I have a 15" screen with 1920x1200. However, a similar resolution on a smaller screen might be a bit more than I want to subject my eyes to. But I don't want to give up screen real estate, either.
Anyways, I've noticed no problems working on the 12", other than the lack of pixels for virtual size (like IDEs and stuff). A 1080p resolution fixes that.