Yes, in more ways than one.
As for dividends, it will have a negative impact but only to an extent. Only a small percentage of firms pay dividends. Furthermore, the research I have seen shows that when dividend taxes go up, firms pay fewer dividends. Every act has a consequence. In the end, the government will be raising less tax revenue because fewer firms will be paying dividends. The government is shooting itself in the foot.
Capital gains taxes have a much more pronounced effect. I am not fully aware of all of the domestic implications but I know in regards to international finance, fewer foreign firms will invest in the U.S. resulting in lower capital inflows into the US.
As for tax rates in general, look at the chart below. People blame Bush for destroying the economy because of lowering tax rates. Notice how net tax revenue increases when tax rates are reduced. Lower taxes can induce economic growth, which leads to more taxable income being generated, which results in higher federal tax revenues. The biggest fallacy I hear from liberals is that Bush's tax policies caused this mess. A quote I read in the WSJ sums my thoughts up regarding that: "Not one economist with an IQ over 60 believes that cutting taxes caused this mess."
This is not to say that increasing taxes is such a horrible thing. It is sometimes needed to slow down an overheated economy. A good example is Clinton's tax increases yet we witnessed an increase in tax revenue. This was possible because the US experienced exceptional economic growth between 1996 and 1999, mostly led by decreased energy costs and the internet bubble.
IMO Taxes must be dynamic and adjusted depending on the overall economic conditions. That said, raising taxes when the economy is tanking is voodoo economics. It will not help the economy grow. Hoover's policies are a good example. IMO Obama is following his path.