PayPal (& eBay) will report your receipts if you have $20,000 or more in volume for a year AND 200 or more transactions.

From PayPal's website:
Under the new legislation, we’ll report to the IRS the total payment volume received by US account holders whose payments exceed both of these levels in a calendar year:

$20,000 USD in gross payment volume from sales of goods or services in a single year
200 payments for goods or services in the same year

The IRS changes apply to all payment processors, including PayPal and include all sales that occur on or after January 1, 2011. Our goal is to help PayPal sellers understand and comply with the new requirements.

Before your payment volume exceeds the reporting thresholds, you’ll be asked to add your tax ID number, such as a Social Security Number (SSN) or Employer Identification Number (EIN), to your existing account(s), if you don’t already have one on file. (Emphasis added)

You can search the PayPal website for "1099" to find this information, as well as other details of how this section works.