I recently saw an article about the sophistication of 'medical marijuana' dispensers, the main focus was this place:

http://sparcsf.org/medicine/flowers

It seems that the beer market could be a good analogy. A few large brands (Bud, Coors, etc) and a thriving micro brew type market. mmm, beer...

The moat for legal marijuana will likely be permitting and regulatory approval to sell. You could see someone like a major tobacco co advocate for strict permitting and regulatory standards to keep the small/individual sellers out. Who knows, probably not worth thinking about unless legalization becomes more widespread.

- matt