The key to being successful or at least make back what you invested is to only mine for about 45-90 days max then sale on eBay.. Then take all the bitcoin you mined plus the money from sales on eBay and upgrade to the next best miner.. This is the only way to keep up with the difficulty rise and stay in the game.. We are getting close to a point where its going to slow down some with the advancement in hashing power making it more modular so you can keep building on what you got allready going. After 20mm miners are more wide spread I see it pretty hard to get much more hashing power for what technology we have available. Under .5 watts per Gh/s will be hard to beat I think...