Blogs were once a vehicle for anti-establishment, noncommercial writers, but now have laid out welcome mats for big corporations. Businesses are spending $50 million to $100 million this year on blog advertising and marketing, said Charlene Li, an analyst at Forrester Research. Blogs have become more mainstream, companies are paying for advertisements or mentions on blogs, courting blog writers with public relations efforts and inviting writers to come blog on one of their corporate sites.