SHANGHAI, March 5 – Last October, a colleague persuaded Xu Jinglei, a Chinese actress and filmmaker, to start writing her own Web log. Now, five months later, Ms. Xu, 31, is the country's most popular blogger, and her runaway success has given rise to an online debate here about the economic value of blogs and who should profit from them. Ms. Xu's blog has already received more than 11 million...