Simply put. If you are selling your own personal stuff, which was purchased at retail and sold for a loss, you don't need to file. On the other end if you are selling for profit, which I hope you all are, you need to file. No matter how small the profit is.
I would imagine a red flag being raised when you finally do hit the paypal 1099 mark. "Oh hey. Look at this guy, he sold $20,000 in his first year if selling on eBay. Must have a knack for it." Remember a tax auditor can search through previous tax years. Hate for anyone to find out the hard way that they should have been paying all along.