I totally see your point (and agree) but there's an important distinction to make in Amazon's case, because there's a big difference between aggressively re-investing your profits into growth and aggressively burning other people's money to grow.
http://www.mondaynote.com/wp-content/uploads/2012/05/Amazon-...
Does this look like a hugely profitable company to you?
[Apple will be an exception here, but they are a very rare case, almost every other growth company looks like Amazon].
Have you accounted for general market trends? Seasonal cycles? Comparisons to other IPOs? Contrast with other types of companies that aren't part of your perceived bubble?
PE isn't everthing but I wish the press would talk more in terms of comparable valuations than the stock dollar price which doesn't really tell you much.