While we can't provide any tax advice (please consult a professional), it's my understanding that you are required to report and (generally) pay taxes on all of your income, including the income from FusionCash, even if it is under $600 in a year (even if it's $20!). The IRS chose the $600 mark for 1099-MISC income for the sake of convenience (a business like ours would drown in paperwork if we had to collect W-9s from every user) but as Mysted mentioned it's completely up to the payer. Some companies will require a W-9 and issue a 1099-MISC for ALL earnings, even small amounts.
In short, (and again - I am not a tax professional and this is not tax advice) you likely have tax liability for your earnings from FusionCash REGARDLESS of the amount. $600 is not a magic number at which point your income becomes taxable - it's just the number at which the IRS wants to keep track of it.