Amazon: Too Expensive, Or More To Come?

Check out this spreadsheet I created, comparing Amazon.com (AMZN) and eBay (EBAY) based on second quarter 2007 numbers. (I had to estimate the eBay employee numbers.)

Is Amazon.com too expensive, or is there more to come? I suppose Amazon has a much bigger market opportunity (retail shifting online) than eBay (auctions must be much closer to maturing). However:

1. Both show continued growth. Is the acceleration at Amazon going to last?

2. The same goes for their core revenue (Media at Amazon, Marketplaces at eBay).

3. Margins at eBay are much fatter, but Amazon is showing a lot of growth. Where are Amazon's margins headed?

4. On most metrics, Amazon is about twice as expensive. How does that compare to growth?

I think the valuation differential is a little stretched, but I do believe Amazon.com demands a premium.