Not just for people and scenes, silhouetting is a time honored photographic style/method in which some elements in the photo are shown in relief - or in partial relief - to the effect that they seem to be silhouettes. See project thread on the utata forum for examples.
Courtesy of Linda/ManyMuses: Some Links to Help
Abode Talks SIlhouettes
Creative Pro (EXCELLENT resource)
adorama
artwolfe tips
Participating in this Utata project is simple! You need to do/have the following three things and then all you have to do is tag your photos utatasilhouette (read about other tagging options) and you're all set! Have fun!