Here is what I found on it's uses in cooking. I seems to be quite the microorganism.
Agar is typically sold as packaged strips of washed and dried seaweed, or in powdered form. Raw agar is white and semi-translucent. For making jelly, it is boiled in water at a concentration of about 0.7-1% w/v (e.g. a 7 gramlitre of water would be 0.7%) until the solids dissolve, after which sweeteners, flavouring, colouring, and pieces of fruit may be added. The agar-agar may then be poured into molds or incorporated into other desserts, such as a jelly layer on a cake. packet of powder into 1
One of the latest fad diets in Asia is the Kanten Diet. Once ingested, kanten triples in size and absorbs water. This results in the consumer feeling more full. Recently this diet has received some press coverage in the United States as well. The diet has shown promise in obesity studies, but agar/kanten has virtually no nutritional value. It is approximately 80% fiber, so part of the diet's effectiveness may be a result of it working as a laxative. There are also some (claimed) effects as to the benefits of agar-agar in controlling diabetes.
I also found a site that mentions vegans in the title, but then starts discussing starches. So I think StirBlue may be right.