This lens was the reason why I switched to Nikon. 
From the moment it was sold I was thrilled that Nikon offers a cheap good macro lens in the normal focal length range.
I have always used this lens in combination with the D200. (Which is a very good camera btw.)

At first I had concerns that the 40mm would be too long for DX Format. But that was not the case. The 40 mm are very nice on APS-C.

A Few impressions in general:

What I like: 
very good image quality over all apertures and distances. I never had an issue with soft corners or CA or any kind of lens shortcomings. TOP!
I like the "Bokeh". The way the unsharp background is rendered is pleasing to my eye. 
Pictures i took with this lens where received very well by everyone.
I rellay enjoyed taking pictures with it!
great colors and contrast!
Is also suitable for photographing people. 
Is quite decently built. it is made mostly from plastic, but it is nice built and the mount is made from metal. 
The Autofocus is very accurate, i used always the center AF point and recomposed. it has an autofocus limiter.   
light and small. This lens is not heavy and not big. but slightly bigger than an 50mm 1,8 for example.
enlargement up to 1:1
price: really cheap for what it is.

What I do not like:
No depth of field scale. i think every fixed focus lens should have this. every!
I was once on the beach, as I have a few grains of sand and salt spray in the focus mechanics come. 
Since then, the manual Focus is hardly to use. But that's not so bad, because the autofocus is better anyway. Still, that shouldnt happen so easily. I guess it would be 
an easy fix to clean it inside, but i dont want to spent the money, because i never really missed the manual focus anyway.
enlargement of 1:1 requires very close aproach to the subject. this will make it more difficult to light properly. but then again, thats not the fault of the lens, 
but a result of the focal lenght

there is no depht of field scale...


the focus limiter is handy


sports a metal lens mount


maximum extension

conclusion:
the 1.8 or 1.4 50mm would be perhabs better for taking portraits and focus faster. But i think the Bokeh is nicer in the 40mm. At least in comparision with the 1.8 AF-D which i own.
But this lens offers jawdropping resolution on every aperture from corner to corner and great colors and contrast and you can take pictrues close up to 1:1 enlargment.
would i recomend this lens for a DX owner? YES!