It's occured to me that online social media technology is moving so fast that any information presented at these conferences will be based on experiences gained in the recent (ancient) past. It's not any fault of the conferences - it's just the reality of the situation. Conferences of this sort seem to be archaic in a time when trends and experiences can be immediately shared online and in near-real-time.
Social media tools themselves present the real opportunity to learn from the pros. Following social media sites (like Mashable.com, as an example) and taking part or even just browsing discussion in specialized sites like Linkedin provide such an in-depth and interactive environment that I really would tend to doubt that most of these conferences are necessary. I think that those that are looking to understand "what it's all about" would be better served by rolling up their sleeves and diving in.