MOST NOTEWORTHY: CBS Corp., Thornburg Mortgage and DiamondRock Hospitality were among today's noteworthy downgrades:

• CBS Corp. (NYSE: CBS) was downgraded to Market Perform from Outperform at Wachovia, citing the weak ad environment and potential M&A strategy to acquire growth, which will limit upside near-term.
  
• Thornburg Mortgage (NYSE: TMA) was downgraded to Underperform from Outperform at Friedman Billings, which said the recent capital raise and related transactions result in 95% dilution, and questions how shares will trade when 2.9B restricted common shares are registered and start trading in mid- May.
  
• DiamondRock Hospitality (NYSE: DRH) was downgraded to Neutral from Outperform at Baird following the company's reduced guidance.

OTHER DOWNGRADES:

• Savvis Inc. (NASDAQ: SVVS) was downgraded to Equal Weight from Overweight at Lehman following the company's Q1 report and guidance.
  
• Memc Electronic Materials (NYSE: WFR) was downgraded to Neutral from Overweight at J.P. Morgan, who cited high Street expectations and a very tight capacity expansion schedule over the next few quarters.