MOST NOTEWORTHY: Vonage Holdings Corp (VG), Boston Scientific Corp (BSX), Sunoco, Inc (SUN) and CV Therapeutics, Inc (CVTX) were some of today's more notable downgrades:

• Vonage Holdings Corp (NYSEL VG) was downgraded to Underperform from Peer Perform at Bear Stearns following the court injunction barring Vonage from using Verizon Communications' (VZ) patented technology.

• Boston Scientific Corp (NYSE: BSX) was cut to Market Perform from Outperform at BMO. Cowen removed Boston Scientific from its Focus List citing superior clinical results from Abbott Laboratories' (ABT) drug-eluting stent, Xience V.

• Deutsche Bank downgraded Sunoco (NYSE: SUN) to Hold from Buy with a $72 target on valuation.

• CV Therapeutics (NASDAQ: CVTX) was downgraded at Deutsche Bank, to Sell from Hold with a $2 target. The downgrade was ahead of the full Ranexa Merlin PIII data to be presented at the American College of Cardiology on Tuesday, March 27th, as the firm believes it will fall short of generating sufficient positive data trends for supporting Ranexa's outlook.

OTHER DOWNGRADES:

• DaimlerChrysler (NYSE: DCX) was removed from JP Morgan's Focus List as the firm believes the potential divestiture of Chrysler is at least partially priced into shares; JP Morgan maintains an Overweight rating on the stock.

• Morgan Stanley cut Progressive Corp (NYSE: PGR) to Underweight from Equal-Weight.

• William Blair downgraded Kronos Inc (NASDAQ: KRON) to Market Perform from Outperform following the company's acquisition.

• Bank of America downgraded Paxar Corp (NYSE: PXR) to Neutral from Buy on news of Avery Dennison Corp's (AVY) acquisition of the company.

• Deutsche Bank cut Tesoro Corp (NYSE: TSO) to Sell from Hold with an $85 target.

• Goldman Sachs cut Volvo (NASDAQ: VOLV) to Neutral from Buy on valuation.

Analyst summaries provided by TheFlyOnTheWall.com (subscription required).

Kronos Incorporated (NASDAQ: KRON), which provides workforce software, agreed to be acquired for $55 per share or $1.8 billion by the private equity firm Hellman & Friedman Capital Partners. That puts a valuation on the firm of about three times revenues.

Founded in 1977, Kronos focuses mostly on mid-size customers, helping them with scheduling, payroll and back-office services. The company charges a license fee for its offerings. Last year, Kronos expanded its business into talent management by acquiring Unicru.

As for Hellman & Friedman, the firm is no stranger to tech deals. Some of its buyouts include DoubleClick and Intergraph.

On news of the deal, Kronos' stock price increased 13.51% to $52.93. Also, the stock is up more than 50% since February.

Tom Taulli is the author of various books, including the Complete M&A Handbook and the EDGAR-Online Guide to Decoding Financial Statements.

MOST NOTEWORTHY: Lear Corp (LEA) and Tellabs Inc (TLAB) were today's most notable upgrades:

• Lear Corp (NYSE: LEA) was upgraded to Neutral from Underperform at Credit Suisse following the $2.31B cash bid from Carl Icahn.

• Merrill Lynch upgraded Tellabs Inc (NASDAQ: TLAB) to Buy from Neutral, citing expectations for an improvement in cross-connect demand and margins; the firm expects Tellabs to benefit from AT&T's (NYSE: T) new broadband initiatives, a demand recovery at Cingular, T-Mobile 3G deployment plans and an increase in Sprint/Nextel (NYSE: S) base stations.

OTHER UPGRADES:

• JP Morgan upgraded Nvidia Corp (NASDAQ: NVDA) to Overweight from Neutral based on expectations for gross margin upside to be driven by improved unit costs and market share gains in the notebook segment.

• Raymond James upgraded shares of AirTran Holdings Inc (NYSE: AAI) to Outperform from Market Perform with a $14 target.

• CIBC upgraded Kronos Inc (NASDAQ: KRON) to Sector Outperformer from Sector Perform, with a $46 target, as they find valuation attractive at current levels given their increasing confidence operations are improving.

• State Street Corp (NYSE: STT) was upgraded to Equal Weight from Underweight at Morgan Stanley following the news of the Investors Financial Services Corp (NASDAQ: IFIN) acquisition.

• Triad Hospitals Inc (NYSE: TRI) was upgraded to Neutral from Sell at Bank of America.

• Overstock.com Inc (NASDAQ: OSTK) was upgraded to Neural from Sell at First Albany, as the worst is already reflected in the stock's valuation.

• Matrix USA upgraded Estee Lauder Co Inc (NYSE: EL) to Hold from Sell based on fundamental trends.

Analyst summaries provided by TheFlyOnTheWall.com (subscription required).