GH/s per watt is everything. I'm pretty sure you're looking at the Sapphire USB miners. These are almost certainly not worth it. If you got 38 of these for f

GH/s per watt is everything. I'm pretty sure you're looking at the Sapphire USB miners. These are almost certainly not worth it. If you got 38 of these for free and had free power and started mining tomorrow, you would have perhaps $1500 worth of BTC a year from now. Assuming you're buying and powering them yourself, you're paying around $1000 and $200 bucks in electricity. It's a fairly risky investment that will likely net you at most $300 on a $1200 outlay. To summarize your purchase: 132 MH/s/watt for ~$1000 If you want to make a better risky investment, you might look into pre-ordering into one of the newer process ASICs, like Butterfly Labs' Monarch: http://www.butterflylabs.com/monarch/ http://www.butterflylabs.com/monarch/ This purchase: 1.71GH/s/watt for $4680 The problem is you're pretty late in the game, so it's really hard to predict what the difficulty rate will look like in even a few months. It's possible that your USB miners will be worthless in a few months due to the mass in flux of newer ASICs. It's also possible that so many people will be purchasing newer ASIC miners that ALL mining will become entirely unprofitable. And all of this assumes the relative stability of the BTC/USD exchange rate. :)