B12 and vegetarianism (by whfoods.com)

The ability of a strict vegetarian diet to supply adequate amounts of B12 remains controversial, despite increasing evidence in support of vegetarianism and its nutritional adequacy. The controversy is fueled by two somewhat divergent schools of thought. One school emphasizes the fact that most animals, including humans, are capable of storing long-term supplies of B12.
In humans, these stores may last for twenty years or longer. Given this potential for storage, a daily requirement for B12 is regarded as highly unlikely.

A second school of thought, however, points to the unreliability of plants as sources of B12. For strict vegetarians who eat no animal products whatsoever, this unreliability may pose a problem. Since no plant is capable of making B-12, the amount of B12 in plant food depends upon the relationship of the plant to soil and root-level microorganisms (bacteria, yeasts, molds, and fungi) which make the vitamin. Cultured and fermented bean products like tofu, tempeh, miso, tamari and shoyu may or may not contain significant amounts of B12, depending upon the bacteria, molds, and fungi used to produce them. The B12 content of sea vegetables also varies according to the distribution of microorganisms in the surrounding sea environment.

Unfortunately, reliable nutrient analyses are often unavailable for consumers of these products, and labeling for B12 content is not required. In general, tofus, tempehs, and sea vegetables tend to be more consistent sources of B12 than misos, tamaris, and shoyus. Depending upon the medium in which they are grown, brewer's and nutritional yeast can also be significant sources of B12 in a strict vegetarian diet.

Info Source: http://www.whfoods.com/genpage.php?tname=nutrient&dbid=107#foodsources