Namaste, Maya:
In fact, there is no rule that says that these Puranas are to be taken seriously and at the same time there is no rule that says that they are to be taken allegorically or metaphorically.
It differs from sect to sect, bhakta to bhakta.
The cool thing, though, out of all of this, is that the "egg origin" story of the universe found in Hinduism is the closest thing to the Big Bang in science. Also, science and Hinduism can, on many grounds, go hand in hand. In fact, many Hindus flood the workforce of Nasa. Hehehe. Funny, right?
Many secularists in the world (especially the ones in the West), and many atheists and agnostics usually "attack" the Abrahamic religions. They see those religions as a hindrance to the development of science. But, Hinduism is never really seen by the imminent scientists in the West as a hindrance. In my opinion, one can find science in Hinduism and Hinduism even in science.