The collapse of Lehman brothers and Stearns was itself a lagging indicator. The issues had already been pressing all the way back to 2007 (see 'housing bubble'). We had clear signs of a stalling economy well before these companies collapsed. The signal these collapses sent, really, was that this was going to be a deeper recession than we had originally hoped.

I don't claim to understand all of this, but my wife (PhD economics) first started sending me warnings about serious economic issues in late 2007.