A lot of people go back and forth on ROI but the way I look at is, all I need to do is break even mining BTC with my block erupters. Nobody is going to make it rich with them but even as the difficulty skyrockets and bitcoin becomes unminable, I will still have the hardware in hand, which I can turn toward any alt sha256 coin. Nobody is considering in their ROI calculations that the physical miner itself has value. You can either sell it for cash or bet on its long term value for mining alt coins.
Erupters will give 0.005, right now. How long will it take to you get ROI back?
I have a few of them, I pay $75 on each... and its not looking good.