I ran several profitability calculators, and even at $85 cost and free electricity, these units don't seem to make any sense.
Even if you consider selling your GPU's, not sure it's a wise strategy to invest cold BTC or Cash to buy Erupters.
By the time they breakeven, they'll be yielding so little profit to even justify the attention to keep them running...and that's assuming they'll survive 10+ months of non-stop mining.
It's more like giving Asicminer an interest-free loan, or betting BTC will be >$500 in next two months, or a combination of both.
Here's how I look at it:
Should you transition away from GPU - definitely yes
Should you hold that money as USD/BTC/ or reinvest in asic - that's a judgement call. The USB erupters are the only asic's on the market that anyone can readily get their hands on in a timely fashion. I bought three when they were first released just to see how consistent they were and how much 'attention' they need (none really).
Long term, either the price of BTC has to continue to climb or the difficulty has to slow down. Right now though, buy-and-mine is probably the most risky bitcoin-related investing strategy.
