I guess hindus themshelves dont know what their religion means by going through the posts. A neighbor near my house had "lakh mahadev puja" and they made lakh siva lingas of clay. I asked to one hindu friend about that and he asked to his priest. The answer I got was that shiva linga is actually the easiest shape that people can make from clay and that is why it has got so much popularity. It also symbolizes that God has not shape. Infact my friend told me that they worship their 'kul devta' also in same manner ie making clay mould. Also people worship stone of any shape as different gods. So according to my friend it has nothing to do with penis and yoni as some people point out. Actually maulavi in my area always said that hindus worship sexual organs etc... but I always took it as his nature i.e islamic nature... but it seems many hindus believe it too. Anyway my friend might be wrong.