Facebook has tons of gun related content. It has open and closed forums. It has topic specific groups for things like 1911s, Glocks, Skeet Shooting or Deer Hunting.
Guns on Facebook can get people in trouble, or actually sell people guns or gear.
Lots of Blogs have corresponding Facbook pages to facilitate communications with readers beyond comments in the Blogs.
Facebook is trying to all things to all people. I can't say I am feeling it will replace my blog. But the one thing it does is get breaking news out FAST.
--Facebook is good and bad. Neither and both.