who is the best person to learn from if i want to learn to be expert in social media? any name sugggestion?
If you check out some backdated issues of .NET magazine (or it's called Practical Web Design in US) I've read some very good articles from a number of industry leaders about social media, including the creator of facebook. Really good read if you want to at least get a head start.
I don't think anyone can claim to be a social media guru. Honestly, almost everything you can do on a social media site can be done by anyone. In order to be successful, you have to be a marketing guru. Anyone who is good and innovative at marketing will succeed in Social Media.