Blog Retreats and Confrences

So I have heard of so many confrences and retreats for bloggers. As I get more serious about my blog, I've been looking into these. But they are very expensive (with travel and hotel and all) So I am just wondering for those that have attended:

What conferences are your favorite?

Are they worth it? Necessary?

What is your favorite part(s)?

Are you learning a lot of new thing that you can only learn at conferences?

Am I missing out? Should I sign up NOW or not?

Anything a newbie should be aware of?

THANKS!