Pinhole images are quite interesting when compared to standard lens images. Along with the obvious difference of "infinite" depth of field and lack of sharp focus, pinhole images lack distortion due to the rectilinear propogation of light. Also, because the light does not travel through glass, pinhole images in color have a vibrancy and richness that lens images do not. Here are some examples.
The two pinholes I'm currently using are both mounted on existing cameras. Several years ago I made a .006" pinhole mounted on a body cap for the Olympus OM4. This pinhole has a focal length of 30mm and a focal ratio of f/200. More recently I constructed a .025" pinhole mounted on a Hasselblad body cap for use on my 503cw. This one has a focal length of 70mm and a focal ratio of f/125.
By using standard cameras, and SLRs specifically, I'm able to forego the usual practices involved with pinhole photography, i.e. the "do it yourself" aspect of loading the camera, dealing with less-than-well-made equipment, etc. Also, I can routinely use color film that I then process at a lab. While there's a certain appeal of the hommade camera, this method works for me. Part of this reason is that with care and patience, I can compose the images in the viewfinder. Perhaps some of the "mystery" is lost this way, but for me, I'm able to create images more like what I visualize.
There's no doubt that using a pinhole camera is very different than using a lens-based camera, but the results are also unique and worth the effort for those interested in producing one-of-a kind images.
To learn more about pinhole photography, check out Pinhole Visions. For a good sample of pinhole photographs from around the world, check out Worldwide Pinhole Day. My image from the 2003 collection can be found at Image #70.