For me, the lag is very noticeable, and occasionally annoying. Not surprisingly, I find it especially bad if the processor is in heavy use by applications.
That said - for me it's worth it. (And I am very picky about UI lag / fluidity). The display is beautiful - everyone goes on about how good images and video look, but pure text is why I have chosen this machine over my 17".
EDIT: I am running Mountain Lion (which is nice, btw), and have graphics switching disabled. 2.6GHz, 16GB.
That said - for me it's worth it. (And I am very picky about UI lag / fluidity). The display is beautiful - everyone goes on about how good images and video look, but pure text is why I have chosen this machine over my 17".
EDIT: I am running Mountain Lion (which is nice, btw), and have graphics switching disabled. 2.6GHz, 16GB.