After tomorrow's difficulty jump, blades will make ~3.25BTC/month assuming 0% difficulty increases thereafter.
So, an erupter USB stick at .5 BTC (333Mh) or so is probably not going to pay for itself with the difficulty going up as it is. And, a blade costing 10.5 BTC (10-13Gh) or so might not as well.
The reasons why people are so game to get in, might be:
Support the network (me)
It is a hobby, if you break even all the merrier. (me)
A more anonymous way of getting your hands on BTC's.
Expecting a much higher BTC price (but even then, buy them now).
Want to take part in the largest social experiment (outside of money itself) of all time. (me)
Personally, I got into a group buy for a 400Gh machine with an October delivery. That probably will be profitable if it arrives in October.
My Jalapeno that was ordered at the beginning of June probably won't break even if it comes later than late September.
My chips ordered through a GB and placed though Yifu, might never come.
A wash?
Lots of chances...
IAS
well, USB miner is so effective, it's profitable even with difficulty around 2 billion (electricity costs at 0.15USD/kWh, 1 BTC at 100 USD), which is 44 times tomorrow's difficulty. You will certainly make your money back (also, they cost 0.32 BTC, not 0.5)
I agree, if you can wait these will pay back