On this blog, I'll use the "beauty in imperfection" explanation I first heard when I encountered the wabi sabi concept. Here's an entry from the Encyclopedia Britannica:
The dual influences of East and West have helped construct a modern Japanese culture that offers familiar elements to the Westerner but that also contains a powerful and distinctive traditional cultural aesthetic. This can be seen, for example, in the intricate detail, miniaturization, and concepts of subtlety that have transformed imported visual art forms. This aesthetic is best captured in the Japanese concept of shibui (literally, “astringent”), or refined understatement in all manner of artistic representation. Closely related are the twin ideals of cultivated simplicity and poverty (wabi) and of the celebration of that which is old and faded (sabi). Underlying all three is the notion of life's transitory and evanescent nature, which is linked to Buddhist thought (particularly Zen) but can be traced to the earliest examples of Japanese literature.
"Japan." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 18 Jan. 2008 <http://search.eb.com/eb/article-23308>.