Many people will say that buying a block erupter is a bad idea because at the rate the network difficulty is rising, they will never produce enough bitcoints to break even.
I had an opportunity to discuss this with a friend today, and the fact is that you can actually still make money with a low yield device like a block erupter, so long as you pay for it in some form of fiat currency. This is true because of the rise in value of bitcoin against these currencies - a trend which is likely to continue.
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-Michael
The issue is not about making a profit in dollars. That mostly depends on the exchange rate. The issue is whether it is better to buy a miner to mine bitcoins or to just buy the bitcoins directly.
Despite what people say, you
can get a positive return on investment with a USB block erupter. The block erupter will mine about 0.015 BTC total, so if you buy one for less than 0.015 BTC (about $5), you will make a profit. It is as simple as that, and it applies to all mining equipment.
You forget electricity charges.....