Usually its $600 and over, however, some sponsors randomly send out 1099's for much smaller amounts, I got one last year for a stainless steel travel mug ($22 ARV)
Yep typically over $600 dollars but the rule usually is if they asked for your SSN on an affy of any sort, or a W-9 to be filled out you are going to be reported to the IRS for that as income.
If you check the IRS' site, they simply state to report prizes under "Other Income". They make no clarification of or exception of the term "prizes". A prize is a prize--add them up and put the total under "Other Income".