The things you need to know you will learn thru experience, which IMO is the best way to learn. There are many, many things you probably will NEVER need to know , so why waste your time with a class ? Focus on things at hand, however for those seeking a broader spectrum of knowledge, a class is OK, but I hate cluttering my mind with stuff that I might never need...
I have however taken classes at The Learning Annex, so I suppose I just shot down my own argument ?