What are the odds that he could solve a block with his USB miners? Thinking in terms of time, how long would it take to get a 25BTC block reward? (That's how that works, right? Newbie, here:-)
1 month, 1 year, 100 years, 1000, years?
As I understand it, it is a bit of luck too, right? A bit like gambling?
You'd want to pool it and get paid for your shares, or run it on an alt chain at much lower difficulty and buy back into BTC ... or likely both.... I'd personally recommend using multipool (us/eu servers available) for small hashers since the pool automatically helps you mine the most cost efficient coin of the day and all you have to do is decide to trade them or keep them and use them as you see fit. Mid-sized miners would do well on bitparking, p2pool or eligius in merge mined configurations to get a slight profits increase and then the large miners probably imho best suited for ghash.io and btcguild .... but that's just my opinion fwiw
but yes... like gambling but gambling in a way that is highly mathematically predictable.