I'm not trying to be mister doom and gloom here, but just want to point out something that some people seem to be missing. The equity markets are not an infinite piggy bank for entrepreneurs. Tesla has been able to raise whatever cash it needed in the past really quickly, so the temptation is to think that this will continue. But if conditions change, like a stock market sell off (October is looming and the whole market looks frothy right now), or Tesla deciding to saddle itself with another money losing business (Solarcity), then it is possible it won't be able to raise money at an acceptable valuation. We know the equity markets were closed to Solarcity already.
You know what happens when companies run out of cash? Yeah, it's the leading cause of bankruptcy (that's a joke, it's effectively the only cause of bankruptcy). Now Tesla has options if it can't raise enough equity, including