The term ‘aliasing’ is a general term applied to signal processing. It refers to an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled. In imaging, it’s often observed as ‘jaggies’, which appear as steps along what should be a continuous line or edge. These are caused by pixel structure. Aliasing can also produce moire, when fine lines appear to ripple due to the interference.
Almost all cameras use a filter (normally in front of the sensor chip) to reduce the visibility of the pixel steps. These filters apply slight blurring to the edges. With high-resolution sensors (10 megapixels or more), the blurring is virtually invisible. You would have to magnify the image a LOT to see any evidence of it. However, it can become visible in low-resolution images, which is why it can be an issue (albeit a very minor one) with video files and when you down-sample images to post them on websites.
The reason Nikon – and more recently, Pentax-Ricoh – have produced cameras without anti-aliasing (AA) filters is to cater for photographers who shoot landscapes and product shots, which are enlarged to make huge displays (usually on screens). This feature has been promoted by both companies and tests have shown there is a small but measurable gain in resolution in cameras without (AA) filters.
At Photo Review we don’t think the average person would notice any difference in pictures used for most applications, even when they are printed at A2 size. Photographers who zoom by cropping and reduce the resolution of their shots may need to be concerned but, again, we doubt they would have the ability to see much difference. And they probably wouldn’t bother looking in the first place.
We have not been even slightly tempted to swap our existing cameras for a camera without an AA filter. A cynic might suggest that the publicity surrounding such cameras is more of a marketing ploy than a genuine attempt to provide improvements for consumers. However, some professional photographers will undoubtedly be able to capitalise on the small resolution gains these cameras yield.
You may be able to find more information in other websites which deal with choosing cameras. http://www.lensrentals.com/blog/category/editorials provides an informative discussion about choosing an SLR. There are plenty of other topics discussed here in an informative and entertaining fashion. Another site we regularly visit is http://www.bythom.com/, which contains lots of good advice on equipment usage and is of particular value to owners of Nikon equipment.