It's future potential that counts, however, not trailing performance.Investors liked some of what they heard with eBay's (EBAY 1.04%) latest quarterly earnings release. A few of the e-commerce veteran's numbers were mildly encouraging -- at least, enough to help the stock outperform the S&P 500 index since they were published at the end of July.One big challenge is that the company is hardly the only e-commerce operator battling to earn your consumer dollar. Will it do well in that endless fight? Let's expl ...