Pros, I have met many photographers on Flickr, groups from my hometown and local area. I can search different groups and get a good idea how a certain camera, film, lens ect will look or perform. I can search different areas that I want to travel to and see pictures of it or ask someone questions about it before I go there. I see a lot of great photographs on there that remind me how much more I need to improve and I am amazed at all of the talent out there. Geo tags.
Cons, I can't really think of any.