Facebook (FB -4.9%) tumbles to new lows; shares are now down 42% from their $38 IPO price. The decline comes after Bernstein's Carlos Kirjner provides a lukewarm upgrade to Market Perform. Kirjner values Facebook's ad business at $19/share, and everything else at a mere $4/share. Moreover, he's worried about a decline in European ad rates (ed: ad rates rose elsewhere), and a share lock-up expiration that begins in August, and will increase Facebook's float by 276% by November. ZNGA -2.3%.