One quick question would we consider facebook a big brand? I think the discussion is focused only on selling a product etc.
Going viral is one of the quickest ways to build a brand whatever it is. How many times have we seen an idea, website, invention go virial and just explode.
All the thoughts ideas are great and worth noting but don't forget the power of the web. One good youtube has created a big brand. One good break and it can happen faster than one would think.
Example EAS is a supplement company they were who are they until a Dallas Cowboy put an eEAS hat on after they won a super bowl, or when a camera caught one of the leading home run hitters Mark with a small bottle in his locker. The company was launched big brand in a matter of days. He sold out a couple years latter. Smart guy he was. Got the big break and got out.