Each weekday, TheStreet.com Ratings updates its ratings on the stocks it covers. The proprietary ratings model projects a stock's total return potential over a 12-month period including both price appreciation and dividends. Buy, hold or sell ratings designate how the Ratings group expects these stocks to perform against a general benchmark of the equities market and interest rates.While the ratings model is quantitative, it uses both subjective and objective elements. For instance, subjective elements include expected equities market returns, future interest rates, implied industry outlook and forecasted company earnings. Objective elements include volatility of past operating revenue, financial strength and company cash flows. Casual dining restaurant chain Kona Grill ( KONA) has been upgraded to hold from sell. The company's revenue jumped 53.7% in the first quarter of fiscal 2007 compared with the same quarter a year earlier, far exceeding the industry average of 11.2%. Kona Grill has been narrowing its losses, losing just 9 cents per share in first quarter of 2007 compared with 16 cents per share a year ealier. Analysts are expecting the company to swing to a profit by fiscal year 2008. If this happens, it could mean additional gains for a stock that has already shot up 40.8% in the past year. Kona Grill had been rated a sell since September 2006. Dutch insurer Aegon ( AEG) has been upgraded to buy from hold. TheStreet.com Ratings feels this company's primary strength is the solid performance of its stock, which is up 17.5% over the past year. AEG shares have gained value, even as earnings have decreased, falling 19.6% in the first quarter of fiscal 2007 compared with the year-earlier period. Aegon still trades at a discount to its peers, with a price-to-earnings ratio of just 10 compared with the insurance industry average of 12.1. This seems to suggest there could be more upside potential. AEG had been rated a hold since March 2006.