Public opinion surveys can be a helpful tool in understanding how people are reactiing to events of the day and some longer-term trends, as long as one is very aware of the limitations of polling methods. How accurately a poll might measure opinions depends on the reliablity of a repesentative sample, the clarity of very specific questions, the margin of error, and the general level of awareness of the public about the issue being surveyed.
Back in October 2008, many people answering the questions of pollsters thought that Republicans then were in the majority of both houses in Congress. It was not true. In fact Democrats were then in the majority in both houses in the previous two years which were also the last two years of the Bush Administration. But apparently many people were confused because they thought the majority in Congress was always the same party as the party of the president, which in 2008 was Republican George W. Bush. For those who follow politics closely, it seems amazing that so many people would not know which party was in control of Congress. But it is not quite as surprising when you consider that people lead their own very busy lives and are often too busy to take the time to be aware of even the most basic facts from the public arena. But these people, informed voters or not, do go to the polls to vote especially in presidential election years when the publicity about candidates is very high.
This general observation brings me back to the level of awareness of the people who are being polled. Do people this year, in 2014, think that Republicans or Democrats control the Congress? If you follow politics, you know that Republicans are the majority in the House and Democrats are the majority in the Senate but this is an unusual balance not often found in the past. The Obama Administration does its best to demonize the House Republicans and give the Senate Democrats a pass on Sen. Harry Reid's chronic inaction on the budget and many issues. But when people hear the word "Congress," they seem to think more about the House than they do the Senate even though Congress is composed of BOTH chambers. Since the president fires almost daily volleys at the House Republicans, my best guess is that people in 2014 are more aware than they were in 2008 that the majority of Congress, at least in the House, is not the party of the president but rather the opposition party which Obama blasts frequently. This could be an advantage to GOP candidates for both the House and Senate in the fall but that does not show up in polls that ask about approval of Congress as an institution or ask about the so-called "generic" ballot as to whether people favor Republicans or Democrats in the fall. By a very small margin, several polls in the Real Clear Politics average of polls give a slight edge to Democrats on the generic ballot. Should those polls be believed with four months still to remain before the November election? Yes and no. If the polls showing a Democratic edge in the generic ballot question are a reflection of general unahppiness with Congress and people also think Congress is controlled by Republicans, then the poll results can just as reasonably be interpreted as a majorty against incumbents which in theory should hurt both parties but in practice usually affects the party of the president in a negative way. In most president administrations of two terms or more since 1932, the party of the president usually loses seats in Congress in the sixth year (or second non-presidential election year). So the party challenging the president in his sixth year in power tends to have history in its favor. If you add to that historical record the fact that President Obama's negative approval ratings have hardened and there is little he can do on his own, in spite of his Eexecutive action bravado, to influence domestic and foreign events, the wind in favor of GOP candidates looks stronger than even in 2010.
The factor most favoring Republican House candidates in 2010 was the energy of the Tea Party which is still very active in spite of premature obituaries. In 2014 also, the energy of the Tea Party already has been a factor even in primaries and will also be a factor on Election Day on Nov. 4.
So should conservative Republicans worry too much about generic polls that show a small Democratic edge? In genreal, no they do not give an accurate projection of how voters will vote for or against incumbents in their own districts. Just be aware of the limitations of polling and you will get a better understanding of how they work.