Amazon mania: Stock hits all-time high

Shares of Amazon reached an all-time high Thursday as investors bid up the stock in anticipation of the company's announcement of additions to its Kindle tablet line (CNET's live blog of the event starts at 10 a.m.). Amazon's stock is up more than 43 percent for the year. In part, the stock is climbing on the assumption that gross profit margins are going to continue to increase. During Amazon's second quarter, gross profits margins widened to 26.1 percent from 24.1 percent, which surpassed Wall Street's expectations for the company. At least for now, that calmed the critics who pointed to the continuing heavy investments in marketing, infrastructure, and fulfillment.

To the critics, Amazon's amazing stock run continues to bewilder. they point to several metrics -- including a price/book ratio of 14.77 and a price/sales ratio of 2.04, both of which are relatively high -- as evidence that investors are, well, more than irrationally exuberant. But while the numbers say one thing, the market continues to like Amazon's story and keeps bidding up its shares.

In early afternoon trading, Amazon's stock was up more than 2 precent to $251.26.

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