Earnings beat expectations, but the outlook was too murky for investors in this high-priced stock.Shares of Monolithic Power Systems (MPWR -17.37%) plunged on Thursday, down 18.2% as of 1:39 p.m. ET.The company reported earnings last night, and while reported results showed strong growth beating expectations, Monolithic's fourth-quarter outlook may have disappointed. Furthermore, the company received an ominous downgrade today.A beat, but perhaps fleetingIn the third quarter, Monolithic reported revenue gro ...