http://n-gate.com/hackernews/ nailed this bit last week:

> A financial website documents Tesla's overvaluation, while explicitly noting that Tesla cannot compete with real automakers in any sense. The company's valuation is recognized to be so high purely because Elon Musk is our lord and savior.

GM's market share is 17.5% while Tesla's is just 0.2%. There's a lot of hope priced into that stock.