"Opportunities" is not "arbitrage". The value of an item going up over time is not disproof of a market's efficiency; efficiency is a point-in-time characteristic, not an across-time characteristic. A market is not required to be psychic to be efficient. It especially doesn't pertain to the case where someone generates value; Warren Buffet is not a passive purchaser of stocks, Warren Buffet seeks out stocks where he can generate value in some manner with better management.

As for your positive returns, the easiest explanation is that you're in a green square on this graph (suitably updated): http://www.nytimes.com/interactive/2011/01/02/business/20110... (Read what the graph is carefully, most people misinterpret it at first glance.)