I am using this Nikon 50mm f/1.4D lens with my Nikon D40. Due to the lack of a focus motor on the body this lens is manual focus only, but otherwise works fine (Metering etc.). Nikon have recently released a f/1.4G model of this lens which will auto-focus on the D40/D60 and should be available around Nov-Dec 2008. Manual focus doesn't bother me so I purchased this lens rather than waiting.
Due to the cropped DX sensor on the D40, this 50mm prime gives approx. 75mm coverage, making it suitable for portraits but makes it a little tricky to get a good shot in a confined room.
As such, I contemplated getting the Sigma 30mm f1.4 EX DC HSM Digital Lens For Nikon Mount
in order to get a bit of a wider angle, but decided against due to its weight (430g, as opposed to this lens which is 230g) and price (around £100 more expensive).
I already own the Sigma DC 3,5-6,3/18-200 OS HSM for Nikon
which is great as a general purpose lens; my main reason for purchasing this Nikon prime was in order to get a wider aperture (f/1.4) and sharper pictures.
At f/1.4 images can be a tad soft, but at f/1.8 (and especially around f/2-2.8) quality is superb. I'd argue that at f/1.8 the image is sharper than Nikon's other popular prime, the Nikon - AF 50mm F/1.8D Lens
. The only other criticism I can find is that it can be prone to lens flare, which is possibly alleviated by getting a petal-hood for it.
Ultimately this is a great prime lens but before purchasing I'd recommend comparing and possibly considering the cheaper Nikon 50mm f/1.8D or the new 50mm f/1.4G which will autofocus on the D40/D60.