I think Ebay is a tough short. Unless some accounting scandal surfaces, Ebay looks more like THE core long in the whole internet sector. Shorting off valuation concerns is a difficult proposition. Valuation typically becomes a shortable proposition when companies are missing estimates or lowering guidance. Not the case with Ebay.
As Seanote said, Ebay has shown impressive relative strength while the rest of Nasdaq has been getting blasted. I think there are solid reasons for this. Ebay has become a category killer, just as great winners like HD, WMT, MSFT and CSCO were. It is very scalable and can work in any country. It will eventually kill classified advertising in newspapers. It has the potential to attract huge advertising rev's, even as other internet portals such as Yahoo and AOL are lsoing advertising rev's.